drm/mediatek: Add Mediatek framebuffer device

For Mediatek drm driver, use fbdev emulation to create a framebuffer
device.
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_drm_drv.c

@@ -15,6 +15,7 @@
 #include <drm/drmP.h>
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_fb_helper.h>
 #include <drm/drm_gem.h>
 #include <drm/drm_gem_cma_helper.h>
 #include <drm/drm_of.h>
@@ -378,6 +379,10 @@ static int mtk_drm_bind(struct device *dev)
 	if (ret < 0)
 		goto err_deinit;
 
+	ret = drm_fbdev_generic_setup(drm, 32);
+	if (ret)
+		DRM_ERROR("Failed to initialize fbdev: %d\n", ret);
+
 	return 0;
 
 err_deinit: