target: linux: select ADK_LINUX_KERNEL_MISC_FILESYSTEMS

Newer kernels hide CONFIG_UBIFS_FS behind CONFIG_MISC_FILESYSTEMS.
Select it when needed.

Signed-off-by: Phil Sutter <phil@nwl.cc>

target/linux/config/Config.in.fs

@@ -273,6 +273,7 @@ config ADK_LINUX_KERNEL_MTD_UBI
 config ADK_LINUX_KERNEL_UBIFS_FS
 	tristate "UBIFS Filesystem"
 	select ADK_LINUX_KERNEL_MTD_UBI
+	select ADK_LINUX_KERNEL_MISC_FILESYSTEMS
 	help
 	  UBIFS is a file system for flash devices which works on top of UBI.