drm/amd/display: Only set default brightness for OLED

[Why]
We used to unconditionally set backlight path as AUX for panels capable
of backlight adjustment via DPCD in set default brightness.

[How]
This should be limited to OLED panel only since we control backlight via
PWM path for SDR mode in LCD HDR panel.
Reviewed-by: Krunoslav Kovac <krunoslav.kovac@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Camille Cho <Camille.Cho@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c

@@ -4914,9 +4914,7 @@ bool dc_link_set_default_brightness_aux(struct dc_link *link)
 {
 	uint32_t default_backlight;
 
-	if (link &&
-		(link->dpcd_sink_ext_caps.bits.hdr_aux_backlight_control == 1 ||
-		link->dpcd_sink_ext_caps.bits.sdr_aux_backlight_control == 1)) {
+	if (link && link->dpcd_sink_ext_caps.bits.oled == 1) {
 		if (!dc_link_read_default_bl_aux(link, &default_backlight))
 			default_backlight = 150000;
 		// if < 5 nits or > 5000, it might be wrong readback