x86: add intel microcode entries to grub config

Create initrd enries for x86 images, that'll load intel microcode as
early as possible. To achieve that the test module for grub is enabled
which provides shell-like conditionals. Also restrict the late load of
microcode to AMD processors.

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>

target/linux/x86/base-files/lib/preinit/02_load_x86_ucode

@@ -2,9 +2,11 @@
 # Copyright (C) 2018 OpenWrt.org
 
 do_load_x86_ucode() {
+	if grep -q AuthenticAMD /proc/cpuinfo; then
 		if [ -e "/sys/devices/system/cpu/microcode/reload" ]; then
 			echo 1 > /sys/devices/system/cpu/microcode/reload
 		fi
+	fi
 }
 
 boot_hook_add preinit_main do_load_x86_ucode

target/linux/x86/image/Makefile

@@ -9,8 +9,8 @@ include $(INCLUDE_DIR)/image.mk
 
 export PATH=$(TARGET_PATH):/sbin
 
-GRUB2_MODULES = biosdisk boot chain configfile ext2 linux ls part_msdos reboot serial vga
-GRUB2_MODULES_ISO = biosdisk boot chain configfile iso9660 linux ls part_msdos reboot serial vga
+GRUB2_MODULES = biosdisk boot chain configfile ext2 linux ls part_msdos reboot serial test vga
+GRUB2_MODULES_ISO = biosdisk boot chain configfile iso9660 linux ls part_msdos reboot serial test vga
 GRUB_TERMINALS =
 GRUB_SERIAL_CONFIG =
 GRUB_TERMINAL_CONFIG =

target/linux/x86/image/grub-iso.cfg

@@ -7,4 +7,7 @@ set root='(cd)'
 
 menuentry "@TITLE@" {
 	linux /boot/vmlinuz @CMDLINE@ noinitrd
+	if [ -s /boot/intel-ucode.img ]; then
+		initrd /boot/intel-ucode.img
+	fi
 }

target/linux/x86/image/grub.cfg

@@ -7,6 +7,9 @@ set root='(@ROOT@)'
 
 menuentry "@TITLE@" {
 	linux /boot/vmlinuz @CMDLINE@ noinitrd
+	if [ -s /boot/intel-ucode.img ]; then
+		initrd /boot/intel-ucode.img
+	fi
 }
 menuentry "@TITLE@ (failsafe)" {
 	linux /boot/vmlinuz failsafe=true @CMDLINE@ noinitrd