ip806x: nbg6817: sysupgrade support both targets for kernel/ rootfs partitions

With this commit and the previous "nbg6817: don't hardcode the rootfs location
by using append-rootblock instead" applied, it is possible to boot- and
sysupgrade from both dual-boot sets (the primary mmcblk0p4+mmcblk0p5 or the
alternative mmcblk0p7+mmcblk0p8). However the sysupgrade support does not
toggle between both dual-boot sets between firmware upgrades so far.

The partition map of the eMMC used in the nbg6817 is:

Found valid GPT with protective MBR; using GPT.
Disk /dev/mmcblk0: 7471104 sectors, 3.6 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): XXX
Partition table holds up to 12 entries
First usable sector is 34, last usable sector is 7471070
Partitions will be aligned on 2-sector boundaries
Total free space is 1 sectors (512 bytes)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              34            8225   4.0 MiB     FFFF  rootfs_data
   2            8226           16417   4.0 MiB     FFFF  romd
   3           16418           18465   1024.0 KiB  FFFF  header
   4           18466           26657   4.0 MiB     FFFF  kernel
   5           26658          157729   64.0 MiB    FFFF  rootfs
   6          157730          159777   1024.0 KiB  FFFF  header_1
   7          159778          167969   4.0 MiB     FFFF  kernel_1
   8          167970          299041   64.0 MiB    FFFF  rootfs_1
   9          299042          823329   256.0 MiB   FFFF  bu1
  10          823330         7471069   3.2 GiB     FFFF  bu2

rootfs_data is the ext4 formatted overlay of the OEM firmware, LEDE
ignores it due to its (too) small size.

romd/ bu1 are initialized with zeroes (0x00) and unused.

bu2 is formatted with ext4 and used for streamboost and other optional
functionality by the OEM firmware, it is reformatted during factory
resets of the OEM firmware.

header/ header_1 contains version information for the corresponding
vendor firmwares installed to kernel/rootfs or kernel_1/ rootfs_1, the
format hasn't been completely reverse engineered so far and remains
left untouched by LEDE:

V1.00(ABCS.2)C0:
 00000000  00 00 a7 74 01 32 f0 00  56 31 2e 30 30 28 41 42  |...t.2..V1.00(AB|
 00000010  43 53 2e 32 29 43 30 00  ff ff ff ff ff ff ff ff  |CS.2)C0.........|
 00000020  ff ff ff ff ff ff ff ff  00 00 d5 dc 4e 42 47 36  |............NBG6|
 00000030  38 31 37 00 ff ff ff ff  ff ff ff ff ff ff ff ff  |817.............|
 00000040  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
 *
 00000060  ff ff ff ff ff ff ff ff  ff ff ff ff 00 00 22 a3  |..............".|
 00000070  00 1c 70 00 ff ff ff ff  ff ff ff ff ff ff ff ff  |..p.............|
 00000080  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
 *
 00000800  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
 00100000

V1.00(ABCS.5)C0:
 00000000  00 00 bf 94 01 46 d8 00  56 31 2e 30 30 28 41 42  |.....F..V1.00(AB|
 00000010  43 53 2e 35 29 43 30 00  ff ff ff ff ff ff ff ff  |CS.5)C0.........|
 00000020  ff ff ff ff ff ff ff ff  00 00 d6 5a 4e 42 47 36  |...........ZNBG6|
 00000030  38 31 37 00 ff ff ff ff  ff ff ff ff ff ff ff ff  |817.............|
 00000040  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
 *
 00000060  ff ff ff ff ff ff ff ff  ff ff ff ff 00 00 c0 2c  |...............,|
 00000070  00 1c 58 00 ff ff ff ff  ff ff ff ff ff ff ff ff  |..X.............|
 00000080  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
 *
 00010000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
 00100000

Signed-off-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>

target/linux/ipq806x/base-files/lib/upgrade/zyxel.sh

@@ -75,10 +75,21 @@ zyxel_do_upgrade() {
 	[ -b "${rootfs}" ] || return 1
 	case "$board" in
 	nbg6817)
-		kernel=mmcblk0p4
+		case "$rootfs" in
+			"/dev/mmcblk0p5")
+				kernel=mmcblk0p4
+			;;
+			"/dev/mmcblk0p8")
+				kernel=mmcblk0p7
+			;;
+			*)
+				return 1
+			;;
+		esac
 		;;
 	*)
 		return 1
+		;;
 	esac
 
 	zyxel_do_flash $tar_file $board $kernel $rootfs