arm64: dts: hikey: Add the SYS_5V and the VDD_3V3 regulators

Add these regulators to better describe the HW, but also because those is
needed in following changes.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>