i965: Just use a uint32_t context handle rather than a malloc'd wrapper.

i965: Just use a uint32_t context handle rather than a malloc'd wrapper.

drm_bacon_context is a malloc'd struct containing a uint32_t context ID
and a pointer back to the bufmgr.  The bufmgr pointer is pretty useless,
as everybody already has brw->bufmgr.  At that point...we may as well
just use the ctx_id handle directly.  A number of places already had to
call drm_bacon_gem_context_get_id() to extract the ID anyway.  Now they
just have it.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>