drm/dp: Add smooth brightness register bit definition

Add DP_EDP_SMOOTH_BRIGHTNESS register bit definition for
EDP_GENERAL_CAPABILITY 2 register.

--v2
-Add eDP 2.0 comment [Ankit]

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://lore.kernel.org/r/20250411060235.2732060-2-suraj.kandpal@intel.com

Author: surajk8

include/drm/display/drm_dp.h

@@ -1025,6 +1025,7 @@
 #define DP_EDP_GENERAL_CAP_2		    0x703
 # define DP_EDP_OVERDRIVE_ENGINE_ENABLED		(1 << 0)
 # define DP_EDP_PANEL_LUMINANCE_CONTROL_CAPABLE		(1 << 4)
+# define DP_EDP_SMOOTH_BRIGHTNESS_CAPABLE		(1 << 6) /* eDP 2.0 */
 
 #define DP_EDP_GENERAL_CAP_3		    0x704    /* eDP 1.4 */
 # define DP_EDP_X_REGION_CAP_MASK			(0xf << 0)