[XFS] Cleanup lock goop.

Switch last couple lock_t's to spinlock_t's. Remove now-unused
spinlock-related macros & types.

SGI-PV: 970382
SGI-Modid: xfs-linux-melb:xfs-kern:29748a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Donald Douwsma <donaldd@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>