arm64: rpi4: gpio: Add brcm,bcm2711-gpio compatible

Looks like we never enabled the main gpio controller on the RPI4 board.
Now gpio are usable.

Approved by: re (gjb)
MFC after: 3 days

(cherry picked from commit 2551d928501fb613dba09b7ffe7e383dba276ca6)
(cherry picked from commit 796faf365c0ea0f50f5138ff8fa62fe48ff3ef71)