drm/i915/vlv: reset VLV media force wake request register

drm/i915/vlv: reset VLV media force wake request register

Media force wake get hangs the machine when the system is booted without
displays attached. The assumption is that (at least some versions of)
the firmware has skipped some initialization in that case.

Empirical evidence suggests we need to reset the media force wake
request register in addition to the render one to avoid hangs.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75895
Reported-by: Imre Deak <imre.deak@intel.com>
Reported-by: Darren Hart <dvhart@linux.intel.com>
Tested-by: Darren Hart <dvhart@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>