BCM270X_DT: Add bcm2835-pm-wdt and bcm2835-rng

This makes it possible to use the mainline watchdog and
random generator drivers:
dtparam=watchdog=on
dtparam=random=on

bcm2708_wdog and bcm2708-rng can still be used.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>