drm/medaitek: add layer_nr for ovl private data

This patch add layer_nr for ovl private data
ovl_2l almost same with with ovl hardware, except the
layer number for ovl_2l is 2 and ovl is 4.
this patch is a preparation for ovl-2l and
ovl share the same driver.
Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_disp_ovl.c

@@ -52,6 +52,7 @@
 struct mtk_disp_ovl_data {
 	unsigned int addr;
 	unsigned int gmc_bits;
+	unsigned int layer_nr;
 	bool fmt_rgb565_is_0;
 };
 
@@ -129,7 +130,9 @@ static void mtk_ovl_config(struct mtk_ddp_comp *comp, unsigned int w,
 
 static unsigned int mtk_ovl_layer_nr(struct mtk_ddp_comp *comp)
 {
-	return 4;
+	struct mtk_disp_ovl *ovl = comp_to_ovl(comp);
+
+	return ovl->data->layer_nr;
 }
 
 static void mtk_ovl_layer_on(struct mtk_ddp_comp *comp, unsigned int idx)
@@ -334,12 +337,14 @@ static int mtk_disp_ovl_remove(struct platform_device *pdev)
 static const struct mtk_disp_ovl_data mt2701_ovl_driver_data = {
 	.addr = DISP_REG_OVL_ADDR_MT2701,
 	.gmc_bits = 8,
+	.layer_nr = 4,
 	.fmt_rgb565_is_0 = false,
 };
 
 static const struct mtk_disp_ovl_data mt8173_ovl_driver_data = {
 	.addr = DISP_REG_OVL_ADDR_MT8173,
 	.gmc_bits = 8,
+	.layer_nr = 4,
 	.fmt_rgb565_is_0 = true,
 };