ARM: dts: bcm2835/bcm2711: Introduce reg-names in watchdog node

bcm2835-pm's bindings now support explicitly setting 'reg-names,' so use
them.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>