cmd: add wdt command

Add a command to control the watchdog devices. This is useful if the
watchdog is rather long running (eg. seconds) and it should be
controlled by scripts. It is also handy during debugging.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 0b07b3b..2bdbfcb 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1101,6 +1101,12 @@
 	help
 	  VirtIO block device support
 
+config CMD_WDT
+	bool "wdt"
+	depends on WDT
+	help
+	  This provides commands to control the watchdog timer devices.
+
 config CMD_AXI
 	bool "axi"
 	depends on AXI