drm/i915: Do not serialize forcewake acquire across domains

On platforms with multiple forcewake domains it seems more efficient
to request all desired ones and then to wait for acks to avoid
needlessly serializing on each domain.

v2: Rebase.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1460045074-1006-1-git-send-email-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/intel_uncore.c

@@ -115,8 +115,10 @@ fw_domains_get(struct drm_i915_private *dev_priv, enum forcewake_domains fw_doma
 	for_each_fw_domain_masked(d, fw_domains, dev_priv) {
 		fw_domain_wait_ack_clear(d);
 		fw_domain_get(d);
-		fw_domain_wait_ack(d);
 	}
+
+	for_each_fw_domain_masked(d, fw_domains, dev_priv)
+		fw_domain_wait_ack(d);
 }
 
 static void