[XFS] simplify xfs_create/mknod/symlink prototype

Simplify the prototype for xfs_create/xfs_mkdir/xfs_symlink by not passing
down a bhv_vattr_t that just hogs stack space. Instead pass down the mode
in a mode_t and in case of xfs_create the rdev as a scalar type as well.

SGI-PV: 968563
SGI-Modid: xfs-linux-melb:xfs-kern:29794a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>