[XFS] Move compat ioctl structs & numbers into xfs_ioctl32.h

This makes the c file less cluttered and a bit more
readable.   Consistently name the ioctl number
macros with "_32" and the compatibility stuctures
with "_compat."  Rename the helpers which simply
copy in the arg with "_copyin" for easy identification.

Finally, for a few of the existing helpers, modify them
so that they directly call the native ioctl helper
after userspace argument fixup.

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>