drm: rockchip: export functions needed by rockchip dw_hdmi bridge driver

To build the rockchip dw_hdmi driver as a module, the
rockchip_drm_encoder_get_mux_id and rockchip_drm_crtc_mode_config
functions need to be exported.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
index a798c7c..21a481b 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
@@ -390,6 +390,7 @@
 
 	return -EINVAL;
 }
+EXPORT_SYMBOL_GPL(rockchip_drm_encoder_get_mux_id);
 
 static int compare_of(struct device *dev, void *data)
 {