i965: Call brw_cache_flush_for_render in predraw_resolve_framebuffer

This makes sure we flush things out of other caches prior to using a
surface through the render cache.  Currently, this is a no-op because GL
won't let you bind anything other than a color surface as color so it
should never end up in the depth cache.  However, this does complete the
flush/add_bo pair for regular drawing which will be required for the
next commit.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "17.3" <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 622786c2)