drm/i915/skl: Enable Per context Preemption granularity control

Per context preemption granularity control is only available from SKL:E0+

Actual WA is to disable percontext preemption granularity control until D0
which is the default case so this is equivalent to the inverse of
WaDisablePerCtxtPreemptionGranularityControl:skl

v2: add some detail to commit msg (Chris)

Reviewed-by: Nick Hoath <nicholas.hoath@intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453412634-29238-8-git-send-email-arun.siluvery@linux.intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index c51e7e9..65e32a3 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -5995,6 +5995,9 @@
 #define SKL_DFSM_CDCLK_LIMIT_450	(2 << 23)
 #define SKL_DFSM_CDCLK_LIMIT_337_5	(3 << 23)
 
+#define GEN7_FF_SLICE_CS_CHICKEN1	_MMIO(0x20e0)
+#define   GEN9_FFSC_PERCTX_PREEMPT_CTRL	(1<<14)
+
 #define FF_SLICE_CS_CHICKEN2			_MMIO(0x20e4)
 #define  GEN9_TSG_BARRIER_ACK_DISABLE		(1<<8)