locks: convert posix locks to file_lock_context

fs/ceph/locks.c

fs/cifs/file.c

fs/lockd/svcsubs.c

fs/locks.c

fs/nfs/delegation.c

fs/nfs/nfs4state.c

fs/nfs/pagelist.c

fs/nfs/write.c

fs/nfsd/nfs4state.c

fs/read_write.c

include/linux/fs.h