drm/i915/dsb: Enable DSB for gen12.

Enabling DSB by setting 1 to has_dsb flag for gen12.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: NShashank Sharma <shashank.sharma@intel.com>
Signed-off-by: NAnimesh Manna <animesh.manna@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190920115930.27829-10-animesh.manna@intel.com

drivers/gpu/drm/i915/i915_pci.c

@@ -787,7 +787,8 @@ static const struct intel_device_info intel_elkhartlake_info = {
 		[TRANSCODER_DSI_0] = TRANSCODER_DSI0_OFFSET, \
 		[TRANSCODER_DSI_1] = TRANSCODER_DSI1_OFFSET, \
 	}, \
-	.has_global_mocs = 1
+	.has_global_mocs = 1, \
+	.display.has_dsb = 1
 
 static const struct intel_device_info intel_tigerlake_12_info = {
 	GEN12_FEATURES,