drm/i915/dp: add HAS_DP20 macro

Let's abstract the DP 2.0 feature. Initially just DG2.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/3746e700641bc17eff270569387fe869707d92ed.1631191763.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1641,6 +1641,7 @@ IS_SUBPLATFORM(const struct drm_i915_private *i915,
 #define HAS_IPS(dev_priv)	(IS_HSW_ULT(dev_priv) || IS_BROADWELL(dev_priv))
 
 #define HAS_DP_MST(dev_priv)	(INTEL_INFO(dev_priv)->display.has_dp_mst)
+#define HAS_DP20(dev_priv)	(IS_DG2(dev_priv))
 
 #define HAS_CDCLK_CRAWL(dev_priv)	 (INTEL_INFO(dev_priv)->display.has_cdclk_crawl)
 #define HAS_DDI(dev_priv)		 (INTEL_INFO(dev_priv)->display.has_ddi)