drm/i915: Implement WaDisableEarlyEOT.

There seems to be another clock gating issue which the workaround is
described as:

   "WA: Set 0xE4F0[1] = 1 to disable Early EOT of thread."
Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171216001117.14232-2-rafael.antognolli@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -8146,6 +8146,7 @@ enum {
 #define   PARTIAL_INSTRUCTION_SHOOTDOWN_DISABLE	(1<<8)
 #define   STALL_DOP_GATING_DISABLE		(1<<5)
 #define   THROTTLE_12_5				(7<<2)
+#define   DISABLE_EARLY_EOT			(1<<1)
 
 #define GEN7_ROW_CHICKEN2		_MMIO(0xe4f4)
 #define GEN7_ROW_CHICKEN2_GT2		_MMIO(0xf4f4)

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1272,6 +1272,9 @@ static int cnl_init_workarounds(struct intel_engine_cs *engine)
 	if (ret)
 		return ret;
 
+	/* WaDisableEarlyEOT:cnl */
+	WA_SET_BIT_MASKED(GEN8_ROW_CHICKEN, DISABLE_EARLY_EOT);
+
 	return 0;
 }