m68k/m68knommu: Implement __get_user_unaligned/__put_user_unaligned()

fs/btrfs/ioctl.c: In function ‘btrfs_ioctl_file_extent_same’:
fs/btrfs/ioctl.c:2802: error: implicit declaration of function ‘__put_user_unaligned’

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>