arm64: dts: rockchip: Add GPU power domain regulator dependency for RK3588

Enabling the GPU power domain requires that the GPU regulator is
enabled. The regulator is enabled at boot time, but automatically
gets disabled when there are no users.

If the GPU driver is not probed at boot time or rebound while
the system is running the system will try to enable the power
domain before the regulator is enabled resulting in a failure
hanging the whole system. Avoid this by adding an explicit
dependency.

Reported-by: Adrián Martínez Larumbe <adrian.larumbe@collabora.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Adrian Larumbe <adrian.larumbe@collabora.com> # On Rock 5B
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>