OMAP: DSS2: Delay regulator_get() calls

DSS submodules DPI/SDI/DSI/VENC require a regulator to function.
However, if the board doesn't use, say, SDI, the board shouldn't need to
configure vdds_sdi regulator required by the SDI module.

Currently the regulators are acquired when the DSS driver is loaded.
This means that if the kernel is configured with SDI, vdds_sdi regulator
is needed for all boards.

This patch changes the DSS driver to acquire the regulators only when a
display of particular type is initialized. For example, vdds_sdi is
acquired when sdi_init_display() is called.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/omap2/dss/dpi.c b/drivers/video/omap2/dss/dpi.c
index 746f1b6..026702b 100644
--- a/drivers/video/omap2/dss/dpi.c
+++ b/drivers/video/omap2/dss/dpi.c
@@ -303,19 +303,24 @@
 {
 	DSSDBG("init_display\n");
 
+	if (cpu_is_omap34xx() && dpi.vdds_dsi_reg == NULL) {
+		struct regulator *vdds_dsi;
+
+		vdds_dsi = dss_get_vdds_dsi();
+
+		if (IS_ERR(vdds_dsi)) {
+			DSSERR("can't get VDDS_DSI regulator\n");
+			return PTR_ERR(vdds_dsi);
+		}
+
+		dpi.vdds_dsi_reg = vdds_dsi;
+	}
+
 	return 0;
 }
 
 int dpi_init(struct platform_device *pdev)
 {
-	if (cpu_is_omap34xx()) {
-		dpi.vdds_dsi_reg = dss_get_vdds_dsi();
-		if (IS_ERR(dpi.vdds_dsi_reg)) {
-			DSSERR("can't get VDDS_DSI regulator\n");
-			return PTR_ERR(dpi.vdds_dsi_reg);
-		}
-	}
-
 	return 0;
 }