drm: move DP_MAX_DOWNSTREAM_PORTS from i915 to drm core

DP_MAX_DOWNSTREAM_PORTS=0x10 is a vendor-independent constant.
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Oleg Vasilev <oleg.vasilev@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190829114854.1539-1-oleg.vasilev@intel.com

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1178,8 +1178,6 @@ struct intel_hdmi {
 };
 
 struct intel_dp_mst_encoder;
-#define DP_MAX_DOWNSTREAM_PORTS		0x10
-
 /*
  * enum link_m_n_set:
  *	When platform provides two set of M_N registers for dp, we can

include/drm/drm_dp_helper.h

@@ -392,6 +392,8 @@
 # define DP_DS_12BPC		            2
 # define DP_DS_16BPC		            3
 
+#define DP_MAX_DOWNSTREAM_PORTS		    0x10
+
 /* DP Forward error Correction Registers */
 #define DP_FEC_CAPABILITY		    0x090    /* 1.4 */
 # define DP_FEC_CAPABLE			    (1 << 0)