drm/i915/icl: Don't allocate fixed bypass path blocks for ICL

GEN9 onwards bypass path allocation of 4 blocks was needed, as per
hardware design. ICL doesn't require bypass path allocation of 4 DDB
blocks, handling the same in this patch.

v2 (from Paulo):
  - No need for a comment that says what the code already says.
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130134918.32283-2-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -3778,7 +3778,8 @@ skl_ddb_get_pipe_allocation_limits(struct drm_device *dev,
 	ddb_size = INTEL_INFO(dev_priv)->ddb_size;
 	WARN_ON(ddb_size == 0);
 
-	ddb_size -= 4; /* 4 blocks for bypass path allocation */
+	if (INTEL_GEN(dev_priv) < 11)
+		ddb_size -= 4; /* 4 blocks for bypass path allocation */
 
 	/*
 	 * If the state doesn't change the active CRTC's, then there's