meta-ethanolx: Support voltage regulators

Populate voltage regulator sensors to the system. This change make
voltage regulator data accessible over DBus, IPMI, Redfish and
webui-vue.

AMD EthanolX CRB has 4 voltage regulators per each of its CPUs (P0/P1):
-ISL69147 - Px VDD core regulator
-ISL69144 - Px VDD SoC regulator
-ISL68127 - Px VDD Mem / VPP ABCD regulator
-ISL68127 - Px VDD Mem / VPP EFGH regulator

All of these voltage regulators are 1st generation multiphase devices.
They can be covered with a ISL68137 Linux driver initialized with a
"isl68137" parameter, which would bring the necessary "raa_dmpvr1_2rail"
initialization.

The threshold values were spoofed from the original voltage regulators
configuration in the AMD EthanolX CRB.

The "PowerState: On" entity-manager parameter is used to make thresholds
active only when the board is powered on.

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
Change-Id: I123db2e356f525e0d269aef780d34d218209592a