drm/i915/dsb: feature flag added for display state buffer.

Display State Buffer(DSB) is a new hardware capability, introduced
in GEN12 display. DSB allows a driver to batch-program display HW
registers.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190920115930.27829-2-animesh.manna@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1863,6 +1863,8 @@ static inline struct drm_i915_private *pdev_to_i915(struct pci_dev *pdev)
 	(BUILD_BUG_ON_ZERO(!__builtin_constant_p(n)) + \
 	 INTEL_INFO(dev_priv)->gen == (n))
 
+#define HAS_DSB(dev_priv)	(INTEL_INFO(dev_priv)->display.has_dsb)
+
 /*
  * Return true if revision is in range [since,until] inclusive.
  *

drivers/gpu/drm/i915/intel_device_info.h

@@ -135,6 +135,7 @@ enum intel_ppgtt_type {
 	func(has_csr); \
 	func(has_ddi); \
 	func(has_dp_mst); \
+	func(has_dsb); \
 	func(has_fbc); \
 	func(has_gmch); \
 	func(has_hotplug); \