i965: Replace references to stencil region size with buffer size

i965: Replace references to stencil region size with buffer size

It is unwise to use a stencil region's size to determine its
renderbuffer's size, because at region creation we fudge the width and
height to accomodate interleaved rows. (See the comment for MESA_FORMAT_S8
in intel_miptree_create()). Most users of stencil_region->{width,height}
should be converted to use stencil_rb->{Width,Height}.

We have already done the replacement in several locations. This patch
continues the replacement in {brw,gen7}_emit_depthbuffer(). To make those
functions look consistent, I've also done the equivalent replacement for
the depth buffer.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>