sunxi: fix build without ext4 rootfs
The sdcard image generation uses CONFIG_TARGET_ROOTFS_PARTSIZE, which is
currently bound to TARGET_ROOTFS_EXT4FS on this target.
Since the rootfs is squashfs anyway, allow deselecting of the ext4fs
one.
Sort the target list alphabetically while here.
Signed-off-by: Andre Heider <[email protected]>