NFS: More fine grained attribute tracking

Currently, if the NFS_INO_INVALID_ATTR flag is set, for instance by
a call to nfs_post_op_update_inode_locked(), then it will not be cleared
until all the attributes have been revalidated. This means, for instance,
that NFSv4 writes will always force a full attribute revalidation.

Track the ctime, mtime, size and change attribute separately from the
other attributes so that we can have nfs_post_op_update_inode_locked()
set them correctly, and later have the cache consistency bitmask be
able to clear them.

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