MX31: add support for MX31 watchdog

The patch add CONFIG_HW_WATCHDOG to be used
with the internal watchdog timer of the MX31
processor. Two function are exported for the
board maintainers:
	mxc_hw_watchdog_enable
	mxc_hw_watchdog_reset

The board maintainer can decide to use mxc_hw_watchdog_reset as
hw_watchdog_reset, or to implement his own function to reset
the watchdog.
The watchdog timer can be configured with CONFIG_SYS_WD_TIMER_SECS
(value in seconds). The MX31 allows values between 0.5
(CONFIG_SYS_WD_TIMER_SECS = 0) and 128 seconds.

Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/include/asm/arch-mx31/mx31-regs.h b/arch/arm/include/asm/arch-mx31/mx31-regs.h
index 105f7d8..37337f2 100644
--- a/arch/arm/include/asm/arch-mx31/mx31-regs.h
+++ b/arch/arm/include/asm/arch-mx31/mx31-regs.h
@@ -75,6 +75,16 @@
 	u32 test;
 };
 
+/* Watchdog Timer (WDOG) registers */
+#define WDOG_ENABLE	(1 << 2)
+#define WDOG_WT_SHIFT	8
+struct wdog_regs {
+	u16 wcr;	/* Control */
+	u16 wsr;	/* Service */
+	u16 wrsr;	/* Reset Status */
+};
+
+
 #define IOMUX_PADNUM_MASK	0x1ff
 #define IOMUX_PIN(gpionum, padnum) ((padnum) & IOMUX_PADNUM_MASK)