Introduce atomic bitops to manipulate the bits in the nfs_inode structure's
"flags" field.

Using bitops means we can use a generic wait_on_bit call instead of an ad hoc
locking scheme in fs/nfs/inode.c, so we can remove the "nfs_i_wait" field from
nfs_inode at the same time.

The other new flags field will continue to use bitmask and logic AND and OR.
This permits several flags to be set at the same time efficiently.  The
following patch adds a spin lock to protect these flags, and this spin lock
will later cover other fields in the nfs_inode structure, amortizing the cost
of using this type of serialization.

Test plan:
 Millions of fsx ops on SMP clients.
Signed-off-by: Chuck Lever <cel@netapp.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>