drm/i915/bdw: BDW Software Turbo

BDW supports GT C0 residency reporting in constant time unit. Driver
calculates GT utilization based on C0 residency and adjusts RP
frequency up/down accordingly. For offscreen workload specificly,
set frequency to RP0.

Offscreen task is not restricted by frame rate, it can be
executed as soon as possible. Transcoding and serilized workload
between CPU and GPU both need high GT performance, RP0 is a good
option in this case. RC6 will kick in to compensate power
consumption when GT is not active.

v2: Rebase on recent drm-intel-nightly
v3: Add flip timerout monitor, when no flip is deteced within
100ms, set frequency to RP0.

Signed-off-by: Daisy Sun <daisy.sun@intel.com>
[torourke: rebased on latest and resolved conflict]
Signed-off-by: Tom O'Rourke <Tom.O'Rourke@intel.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 127eb0a..e572ffa 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -9757,6 +9757,9 @@
 	unsigned long flags;
 	int ret;
 
+	//trigger software GT busyness calculation
+	gen8_flip_interrupt(dev);
+
 	/*
 	 * drm_mode_page_flip_ioctl() should already catch this, but double
 	 * check to be safe.  In the future we may enable pageflipping from