i965: Get a ralloc context into brw_compile.

i965: Get a ralloc context into brw_compile.

This would be so much easier if we were using C++; we could simply use
constructors and destructors.  Instead, we have to update all the
callers.

While we're at it, ralloc various brw_wm_compile fields rather than
explicitly calloc/free'ing them.

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