NFSv4.1: Don't cache deviceids that have no notifications

The spec says that once all layouts that reference a given deviceid
have been returned, then we are only allowed to continue to cache
the deviceid if the metadata server supports notifications.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --cc fs/nfs/nfs4proc.c
Simple merge

diff --cc fs/nfs/pnfs.h
Simple merge

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