lantiq: Enable the uImage mtd splitter

Until linux 4.1 the lantiq target used CONFIG_MTD_UIMAGE_SPLIT=y. That
option however is only available until linux 4.3 - thus it was not added
to lantiq's 4.4 kernel config (in r48307). This results in broken images
for devices which are using uImages. This fixes #21652

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

SVN-Revision: 48381

target/linux/lantiq/config-4.4

@@ -141,6 +141,7 @@ CONFIG_MTD_SPLIT_BRNIMAGE_FW=y
 CONFIG_MTD_SPLIT_EVA_FW=y
 CONFIG_MTD_SPLIT_FIRMWARE=y
 CONFIG_MTD_SPLIT_TPLINK_FW=y
+CONFIG_MTD_SPLIT_UIMAGE_FW=Y
 CONFIG_NEED_DMA_MAP_STATE=y
 CONFIG_NEED_PER_CPU_KM=y
 CONFIG_NO_GENERIC_PCI_IOPORT_MAP=y