xfs: move kernel specific type definitions to xfs.h

xfs_types.h is shared with userspace, so having kernel specific
types defined in it is problematic. Move all the kernel specific
defines to xfs_linux.h so we can remove the __KERNEL__ guards from
xfs_types.h.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>