arm64: dts: meson-sm1-sei610: enable DVFS

arm64: dts: meson-sm1-sei610: enable DVFS

This enables DVFS for the Amlogic SM1 based SEI610 board by:
- Adding the SM1 SoC OPPs taken from the vendor tree
- Selecting the SM1 Clock controller instead of the G12A one
- Adding the CPU rail regulator, PWM and OPPs for each CPU nodes.

Each power supply can achieve 0.69V to 1.05V using a single PWM
output clocked at 666KHz 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 the cpu 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

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>