arm64: dts: meson-g12b-odroid-n2: enable DVFS

arm64: dts: meson-g12b-odroid-n2: enable DVFS

Enable DVFS for the Odroid-N2 by setting the clock, OPP and supply
for each cores of each CPU clusters.

The first cluster uses the "VDDCPU_B" power supply, and the second
cluster uses the "VDDCPU_A" power supply.

Each power supply can achieve 0.73V to 1.01V using 2 distinct PWM
outputs 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 of each cluster 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>