i965: Split brw_wm_surfaces state into renderbuffer and texture atoms.

i965: Split brw_wm_surfaces state into renderbuffer and texture atoms.

First, the texturing setup code is relevant for all pipeline stages,
while renderbuffer surfaces are only used by the WM.

Secondly, renderbuffer and texture setup depends on a different set of
dirty bits.  There's no reason to walk the array of textures when
changing draw buffers, or vice-versa.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Paul Berry <stereotype441@gmail.com>