drm/amd/display: limit the code change to ips enabled asic

Limit the code change for ips enable to reduce the impact for now. Also
exit_ips first before dc_power_down to avoid 0x9f.

Reviewed-by: Chris Park <[e-mail]>
Acked-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Charlene Liu <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 void dc_power_down_on_boot(struct dc *dc)
 {
 	if (dc->ctx->dce_environment != DCE_ENV_VIRTUAL_HW &&
-			dc->hwss.power_down_on_boot)
+			dc->hwss.power_down_on_boot) {
+
+			if (dc->caps.ips_support)
+				dc_exit_ips_for_hw_access(dc);
+
 		dc->hwss.power_down_on_boot(dc);
+	}
 }
 
 void dc_set_power_state(