arm64: dts: rockchip: Add vcc_sys enable pin on rk3399-roc-pc

rk3399-roc-pc has vcc_sys 5V supply for USB and other peripherals.
Add the GPIO pin to enable the regulator.

Signed-off-by: Markus Reichl <m.reichl@fivetechno.de>
Link: https://lore.kernel.org/r/c72db0ad-c261-af4f-efe6-22bbcf4a0b7b@fivetechno.de


Signed-off-by: Heiko Stuebner <heiko@sntech.de>