drm/i915: Acquire audio powerwell for HD-Audio registers

drm/i915: Acquire audio powerwell for HD-Audio registers

On Haswell/Broadwell, the HD-Audio block is inside the HDMI/display
power well and so the sna-hda audio codec acquires the display power
well while it is operational. However, Skylake separates the powerwells
again, but yet we still need the audio powerwell to setup the registers.
(But then the hardware uses those registers even while powered off???)

Acquiring the powerwell around setting the chicken bits when setting up
the audio channel does at least silence the WARNs from touching our
registers whilst unpowered. We silence our own test cases, but maybe
there is a latent bug in using the audio channel?

v2: Grab both rpm wakelock and audio wakelock

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96214
Fixes: c1948b6450d2 "ALSA: hda - remove dependency on i915 power well for SKL")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Libin Yang <libin.yang@intel.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Marius Vlad <marius.c.vlad@intel.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/1470240540-29004-1-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>