Revert "mvebu: fix initramfs/kernel image for CZNIC Turris Omnia"

This reverts commit e401a2a42e6d7c892e1cf7d765fa5ec9b2db3fb3 as at least
two users had reported breakage on their devices.

References: https://lists.infradead.org/pipermail/openwrt-devel/2020-December/032837.html
References: https://github.com/openwrt/openwrt/commit/e401a2a42e6d7c892e1cf7d765fa5ec9b2db3fb3#commitcomment-45189788
Cc: Karel Kočí <[email protected]>
Reported-by: Magnus Kroken <[email protected]>
Signed-off-by: Petr Štetiar <[email protected]>

target/linux/mvebu/image/cortexa9.mk

@@ -32,7 +32,8 @@ define Device/cznic_turris-omnia
   DEVICE_VENDOR := CZ.NIC
   DEVICE_MODEL := Turris Omnia
   KERNEL_INSTALL := 1
-  KERNEL := kernel-bin | append-dtb
+  KERNEL := kernel-bin
+  KERNEL_INITRAMFS := kernel-bin
   DEVICE_PACKAGES :=  \
     mkf2fs e2fsprogs kmod-fs-vfat kmod-nls-cp437 kmod-nls-iso8859-1 \
     wpad-basic-wolfssl kmod-ath9k kmod-ath10k-ct ath10k-firmware-qca988x-ct \