ARM: imx6 Add WDOG3 for i.MX6SX

There are three wdogs for i.MX 6SoloX. Add wdog3 support
in function imx_set_wdog_powerdown.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>

arch/arm/cpu/armv7/mx6/soc.c

@@ -230,6 +230,11 @@ static void imx_set_wdog_powerdown(bool enable)
 	struct wdog_regs *wdog1 = (struct wdog_regs *)WDOG1_BASE_ADDR;
 	struct wdog_regs *wdog2 = (struct wdog_regs *)WDOG2_BASE_ADDR;
 
+#ifdef CONFIG_MX6SX
+	struct wdog_regs *wdog3 = (struct wdog_regs *)WDOG3_BASE_ADDR;
+	writew(enable, &wdog3->wmcr);
+#endif
+
 	/* Write to the PDE (Power Down Enable) bit */
 	writew(enable, &wdog1->wmcr);
 	writew(enable, &wdog2->wmcr);