mpc85xx: disable initramfs image in TL-WDR4900

Initramfs image isn't required for this device and regular
initramfs generation isn't work properly. It create not working
binaries.

This patch disable initramfs image for TL-WDR4900.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>

target/linux/mpc85xx/image/Makefile

@@ -49,6 +49,7 @@ define Device/tl-wdr4900-v1
   TPLINK_HWREV := 1
   TPLINK_FLASHLAYOUT := 16Mppc
   KERNEL_NAME := cuImage.tl-wdr4900-v1
+  KERNEL_INITRAMFS :=
   SUPPORTED_DEVICES:=tl-wdr4900-v1 tplink,tl-wdr4900-v1
   IMAGES := fdt.bin factory.bin sysupgrade.bin
   IMAGE/fdt.bin := append-dtb