ramips: make Genexis EX400 factory image dependent on initramfs

The factory image generation for the Genexis EX400 image currently fails
if CONFIG_TARGET_ROOTFS_INITRAMFS is disabled.

Create the factory image only if said config option is enabled to avoid
failing builds.

Signed-off-by: David Bauer <mail@david-bauer.net>

Author: blocktrron

target/linux/ramips/image/mt7621.mk

@@ -1403,9 +1403,11 @@ define Device/genexis_pulse-ex400/common
     --log-lebs=2 --space-fixup --squash-uids
   KERNEL := kernel-bin | lzma | uImage lzma
   KERNEL_INITRAMFS := kernel-bin | append-dtb | lzma | uImage lzma
+ifneq ($(CONFIG_TARGET_ROOTFS_INITRAMFS),)
   IMAGES += factory.bin
   IMAGE/factory.bin := append-image-stage initramfs-kernel.bin | \
 	inteno-bootfs | inteno-y3-header EX400 | append-md5sum-ascii-salted
+endif
   IMAGE/sysupgrade.bin := append-kernel | inteno-bootfs | \
     sysupgrade-tar kernel=$$$$@ | check-size | append-metadata
   DEVICE_IMG_NAME = $$(DEVICE_IMG_PREFIX)-$$(2)