drm/amd/display: trigger timing sync only if TG is running

[Why&How]
If the timing generator isnt running, it does not make sense to trigger
a sync on the corresponding OTG. Check this condition before starting.
Otherwise, this will cause error like:

*ERROR* GSL: Timeout on reset trigger!

Fixes: dc55b106 ("drm/amd/display: Disable phantom OTG after enable for plane disable")
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c

@@ -2216,6 +2216,12 @@ void dcn10_enable_vblanks_synchronization(
 		opp = grouped_pipes[i]->stream_res.opp;
 		tg = grouped_pipes[i]->stream_res.tg;
 		tg->funcs->get_otg_active_size(tg, &width, &height);
+
+		if (!tg->funcs->is_tg_enabled(tg)) {
+			DC_SYNC_INFO("Skipping timing sync on disabled OTG\n");
+			return;
+		}
+
 		if (opp->funcs->opp_program_dpg_dimensions)
 			opp->funcs->opp_program_dpg_dimensions(opp, width, 2*(height) + 1);
 	}