arm64: dts: meson-g12a-u200: add regulators

Add system regulators for the S905D U200 reference design.

Add some regulators. Still missing
* VDD_EE (0.8V - PWM controlled)
* VDD_CPU (PWM controlled)

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>