arm64: dts: meson-g12a-x96-max: add regulators

Add system regulators for the X96 Max Set-Top-Box.

Still missing
* VDD_EE (0.8V - PWM controlled)
* VDD_CPU (PWM controlled)

Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>