[Why] Check if the eDP sink supports the dynamic backlight control [How] Query the dynamic backlight capability in DPCD (eDP case only) Signed-off-by: Roy Chan <roy.chan@amd.com> Acked-by: Bindu Ramamurthy <bindu.r@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>