arm64: dts: rockchip: add voltage properties for vcc3v3_pcie on rk3399 ficus

The vcc3v3_pcie regulator supplies 3.3V so add voltage properties
for it.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
[split off from original patch]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>