ramips: add factory image for Netgear R6350

This adds factory image generation for all three
devices. These images can be flashed via WebUI
for easy installation.

Thanks to David Bauer for the inspiration.

Signed-off-by: Christoph Krapp <achterin@googlemail.com>
[altered commit to only include the R6350]
Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ramips/image/mt7621.mk

@@ -421,7 +421,12 @@ define Device/netgear_r6350
   KERNEL_SIZE := 4096k
   IMAGE_SIZE := 40960k
   UBINIZE_OPTS := -E 5
-  IMAGES += kernel.bin rootfs.bin
+  SERCOMM_HWID := CHJ
+  SERCOMM_HWVER := A001
+  SERCOMM_SWVER := 0x0052
+  IMAGES += factory.img kernel.bin rootfs.bin
+  IMAGE/factory.img := pad-extra 2048k | append-kernel | pad-to 6144k | append-ubi | \
+	pad-to $$$$(BLOCKSIZE) | sercom-footer | pad-to 128 | zip $$$$(DEVICE_MODEL).bin | sercom-seal
   IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata
   IMAGE/kernel.bin := append-kernel
   IMAGE/rootfs.bin := append-ubi | check-size $$$$(IMAGE_SIZE)