crc16: Rename fs/ubifs/crc16.h to include/linux/crc16.h

File fs/ubifs/crc16.h is standard linux's crc16.h include file. So move it
from fs/ubifs to include/linux where are also other linux include files.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>