arm64: dts: meson-g12a: add cpus OPP table

arm64: dts: meson-g12a: add cpus OPP table

Add the OPP table taken from the vendor u200 and u211 DTS.

The Amlogic G12A SoC seems to available in 3 types :
- low-speed: up to 1,8GHz
- mid-speed: up to 1,908GHz
- high-speed: up to 2.1GHz

And the S905X2 opp voltages are slightly higher than the S905D2
OPP voltages for the low-speed table.

This adds the conservative OPP table with the S905X2 higher voltages
and the maximum low-speed OPP frequency.

The values were tested to be stable on an Amlogic U200 Reference Board,
SeiRobotics SEI510 and X96 Max Set-Top-Boxes 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

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>