locks: add a dedicated spinlock to protect i_flctx lists

We can now add a dedicated spinlock without expanding struct inode.
Change to using that to protect the various i_flctx lists.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Acked-by: Christoph Hellwig <hch@lst.de>

diff --cc fs/ceph/locks.c
Simple merge

diff --cc fs/cifs/file.c
Simple merge

diff --cc fs/lockd/svcsubs.c
Simple merge

diff --cc fs/locks.c
Simple merge

diff --cc fs/nfs/delegation.c
Simple merge

diff --cc fs/nfs/nfs4state.c
Simple merge

diff --cc fs/nfs/write.c
Simple merge

diff --cc fs/nfsd/nfs4state.c
Simple merge

diff --cc include/linux/fs.h
Simple merge