drm/i915/kbl: Add WaEnableGapsTsvCreditFix

We need this crucial workaround from skl also to all kbl revisions.
Lack of it was causing system hangs on skl enabling so this is
a must have.

v2: Don't add revid checks to gen9 init workarounds (Arun)

References: HSD#2126660
Cc: Arun Siluvery <arun.siluvery@linux.intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465309159-30531-8-git-send-email-mika.kuoppala@intel.com

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1188,12 +1188,17 @@ static int bxt_init_workarounds(struct intel_engine_cs *engine)
 
 static int kbl_init_workarounds(struct intel_engine_cs *engine)
 {
+	struct drm_i915_private *dev_priv = engine->i915;
 	int ret;
 
 	ret = gen9_init_workarounds(engine);
 	if (ret)
 		return ret;
 
+	/* WaEnableGapsTsvCreditFix:kbl */
+	I915_WRITE(GEN8_GARBCNTL, (I915_READ(GEN8_GARBCNTL) |
+				   GEN9_GAPS_TSV_CREDIT_DISABLE));
+
 	return 0;
 }