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