OMAPDSS: add 'has_writeback' flag

At the moment we have a function to get the number of writeback
pipelines supported. However, the function is used in a wrong way,
causing a wrong pipeline to get configured when trying to use WB. Also,
we only have a single writeback pipeline on any of the DSS versions.

To fix and simplify this, create a 'has_writeback' flag into the dispc
driver, and after checking the flag, use OMAP_DSS_WB pipeline
explicitly when calling the configuration functions.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/fbdev/omap2/dss/dispc.c b/drivers/video/fbdev/omap2/dss/dispc.c
index 0cccff2..aa74b3d 100644
--- a/drivers/video/fbdev/omap2/dss/dispc.c
+++ b/drivers/video/fbdev/omap2/dss/dispc.c
@@ -102,6 +102,8 @@
 
 	/* POL_FREQ has ALIGN bit */
 	bool supports_sync_align:1;
+
+	bool has_writeback:1;
 };
 
 #define DISPC_MAX_NR_FIFOS 5
@@ -710,7 +712,6 @@
 {
 	int i;
 	int num_ovl = dss_feat_get_num_ovls();
-	int num_wb = dss_feat_get_num_wbs();
 	const struct color_conv_coef ctbl_bt601_5_ovl = {
 		298, 409, 0, 298, -208, -100, 298, 0, 517, 0,
 	};
@@ -721,8 +722,8 @@
 	for (i = 1; i < num_ovl; i++)
 		dispc_ovl_write_color_conv_coef(i, &ctbl_bt601_5_ovl);
 
-	for (; i < num_wb; i++)
-		dispc_ovl_write_color_conv_coef(i, &ctbl_bt601_5_wb);
+	if (dispc.feat->has_writeback)
+		dispc_ovl_write_color_conv_coef(OMAP_DSS_WB, &ctbl_bt601_5_wb);
 }
 
 static void dispc_ovl_set_ba0(enum omap_plane plane, u32 paddr)
@@ -3562,7 +3563,7 @@
 			DUMPREG(i, DISPC_OVL_ATTRIBUTES2);
 	}
 
-	if (dss_feat_get_num_wbs()) {
+	if (dispc.feat->has_writeback) {
 		i = OMAP_DSS_WB;
 		DUMPREG(i, DISPC_OVL_BA0);
 		DUMPREG(i, DISPC_OVL_BA1);
@@ -3892,6 +3893,7 @@
 	.gfx_fifo_workaround	=	true,
 	.set_max_preload	=	true,
 	.supports_sync_align	=	true,
+	.has_writeback		=	true,
 };
 
 static const struct dispc_features omap54xx_dispc_feats = {
@@ -3914,6 +3916,7 @@
 	.mstandby_workaround	=	true,
 	.set_max_preload	=	true,
 	.supports_sync_align	=	true,
+	.has_writeback		=	true,
 };
 
 static int dispc_init_features(struct platform_device *pdev)