arm64: bcm2835: Add missing dependency on MFD_CORE.

When adding the MFD dependency for power domains and WDT in bcm2835, I
added it only on the arm32 side and missed it for arm64.

Fixes: 5e6acc3e ("bcm2835-pm: Move bcm2835-watchdog's DT probe to an MFD.")
Signed-off-by: Eric Anholt <eric@anholt.net>
Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>

arch/arm64/Kconfig.platforms

@@ -27,6 +27,7 @@ config ARCH_BCM2835
 	bool "Broadcom BCM2835 family"
 	select TIMER_OF
 	select GPIOLIB
+	select MFD_CORE
 	select PINCTRL
 	select PINCTRL_BCM2835
 	select ARM_AMBA