watchdog: armada_37xx: Convert to official DT bindings

Official DT bindings have only one reg property: watchdog address space.
Convert armada-37xx-wdt.c driver to offical DT bindings and access sel_reg
register via MVEBU_REGISTER() macro, as its value (required by U-Boot
driver) is not in DT yet. In later stage can be driver cleaned to not use
it.

This change would allow U-Boot to use A3720 watchdog DTS structure from
Linux kernel.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/watchdog/armada-37xx-wdt.c b/drivers/watchdog/armada-37xx-wdt.c
index 6b5e1ab..2e119b9 100644
--- a/drivers/watchdog/armada-37xx-wdt.c
+++ b/drivers/watchdog/armada-37xx-wdt.c
@@ -155,12 +155,9 @@
 	struct a37xx_wdt *priv = dev_get_priv(dev);
 	fdt_addr_t addr;
 
-	addr = dev_read_addr_index(dev, 0);
-	if (addr == FDT_ADDR_T_NONE)
-		goto err;
-	priv->sel_reg = (void __iomem *)addr;
+	priv->sel_reg = (void __iomem *)MVEBU_REGISTER(0x0d064);
 
-	addr = dev_read_addr_index(dev, 1);
+	addr = dev_read_addr(dev);
 	if (addr == FDT_ADDR_T_NONE)
 		goto err;
 	priv->reg = (void __iomem *)addr;