mpc5200: a4m2k: Implement custom "dynamic" watchdog support

This patch adds a custom U-Boot command "wdogtoggle" which enables the
external hardware watchdog toggling via an GPIO pin on the a4m2k
board. After issuing this commands, the watchdog will be serviced
by U-Boot so that the user can use all U-Boot commands from the
prompt.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/include/configs/a3m071.h b/include/configs/a3m071.h
index d8559d8..13f3226 100644
--- a/include/configs/a3m071.h
+++ b/include/configs/a3m071.h
@@ -166,6 +166,11 @@
 #define CONFIG_SYS_GPS_PORT_CONFIG_2	0x1005C005
 #endif
 
+#define CONFIG_WDOG_GPIO_PIN		GPIO_WKUP_7
+#if defined(CONFIG_A4M2K) && !defined(CONFIG_SPL_BUILD)
+#define CONFIG_HW_WATCHDOG		/* Use external HW-Watchdog	*/
+#endif
+
 /*
  * Configuration matrix
  *                        MSB                          LSB