nfs: move nfs_fhandle_hash to common include file

[ Upstream commit e59fb674 ]

lockd needs to be able to hash filehandles for tracepoints. Move the
nfs_fhandle_hash() helper to a common nfs include file.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Stable-dep-of: cd35b6cb ("nfs: add missing selections of CONFIG_CRC32")
Signed-off-by: Sasha Levin <sashal@kernel.org>