i965/blorp: Add an is_render_target parameter to surface_info::set.

i965/blorp: Add an is_render_target parameter to surface_info::set.

This allows us to determine whether we're setting up a format for
the source (as a texture) or destination (as a render target).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>