drm/i915: Restore GT coarse power gating workaround

The workaround to disable coarse power gating is still needed on SKL
GT3/GT4 machines and since the RC6 context corruption was discovered by
the hardware team also on all GEN9 machines. Restore applying the
workaround.

Fixes: c1132367 ("drm/i915: Extract GT render sleep (rc6) management")
Testcase: igt/intel_gt_pm_late_selftests/live_rc6_ctx
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andi Shyti <andi.shyti@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191114152621.7235-1-imre.deak@intel.com
(cherry picked from commit 980f87a2)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/gt/intel_rc6.c

@@ -178,6 +178,11 @@ static void gen9_rc6_enable(struct intel_rc6 *rc6)
 	    GEN6_RC_CTL_RC6_ENABLE |
 	    rc6_mode);
 
+	/*
+	 * WaRsDisableCoarsePowerGating:skl,cnl
+	 *   - Render/Media PG need to be disabled with RC6.
+	 */
+	if (!NEEDS_WaRsDisableCoarsePowerGating(rc6_to_i915(rc6)))
 		set(uncore, GEN9_PG_ENABLE,
 		    GEN9_RENDER_PG_ENABLE | GEN9_MEDIA_PG_ENABLE);
 }