i965/miptree: Take an isl_format in render_aux_usage

Not all rendering matches the miptree format.  We allow rendering to
texture views so there are cases where it may not match.  In those
cases, our current scheme of just passing the value of ctx->sRGBEnabled
isn't viable.  Instead, just do what we do for texturing and pass the
view format in directly.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Cc: mesa-stable@lists.freedesktop.org
(cherry picked from commit 39c5c12f)
[Andres Gomez: remove code which was trivially modified previously]
Signed-off-by: Andres Gomez <agomez@igalia.com>

Conflicts:
	src/mesa/drivers/dri/i965/brw_draw.c
	src/mesa/drivers/dri/i965/brw_wm_surface_state.c