drm/amd/display: Fix programming backlight on OLED panels

commit 3807756 ("drm/amd/display: Implement new
backlight_level_params structure") adjusted DC core to require
the backlight type to be programmed in the dc link when changing
brightness.  This isn't initialized in amdgpu_dm for OLED panels
though which broke brightness.

Explicitly initialize when aux support is enabled.

Reported-and-tested-by: Luke Jones <[email protected]>
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3792
Fixes: 3807756 ("drm/amd/display: Implement new backlight_level_params structure")
Reviewed-by: Harry Wentland <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mario Limonciello <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: superm1

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -3481,6 +3481,8 @@ static void update_connector_ext_caps(struct amdgpu_dm_connector *aconnector)
 		caps->aux_support = false;
 	else if (amdgpu_backlight == 1)
 		caps->aux_support = true;
+	if (caps->aux_support)
+		aconnector->dc_link->backlight_control_type = BACKLIGHT_CONTROL_AMD_AUX;
 
 	luminance_range = &conn_base->display_info.luminance_range;