arm: bcmbca: replace ARCH_BCM68360 symbols in Kconfig with BCM6856

As CONFIG_ARCH_BCM68360 is replaced with CONFIG_BCM6856, update the
driver Kconfig to use the new config symbol.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Reviewed-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 550bed7..aef6d3f 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -130,7 +130,7 @@
 
 config WDT_BCM6345
 	bool "BCM6345 watchdog timer support"
-	depends on WDT && (ARCH_BMIPS || ARCH_BCM68360 || \
+	depends on WDT && (ARCH_BMIPS || BCM6856 || \
 			   ARCH_BCM6858 || BCM63158 || \
 			   ARCH_BCM6753)
 	help