arm64: dts: meson-g12a: enable DVFS on G12A boards

arm64: dts: meson-g12a: enable DVFS on G12A boards

Enable DVFS for the U200, SEI520 and X96-Max Amlogic G12A based board
by setting the clock, OPP and supply for each CPU cores.

The CPU cluster power supply can achieve 0.73V to 1.01V using a PWM
output clocked at 800KHz with an inverse duty-cycle.

DVFS has been tested by running the arm64 cpuburn at [1] and cycling
between all the possible cpufreq translations and checking the final
frequency using the clock-measurer, script at [2].

[1] https://github.com/ssvb/cpuburn-arm/blob/master/cpuburn-a53.S
[2] https://gist.github.com/superna9999/d4de964dbc0f84b7d527e1df2ddea25f

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