Add support for WNDR3700 and WNDR3700v2.
They share most things with WNDR3800.
Only device IDs and partition structure needs to be set.
Note: WNDR3700 (v1) has no NETGEAR_HW_ID, but has
also the NA version of the factory image.
Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>
