ARM: dts: amlogic: meson8-fernsehfee3: Describe regulators

ARM: dts: amlogic: meson8-fernsehfee3: Describe regulators

The fernsehfee3 board uses a Ricoh RN5T618 PMIC to generate various
voltages. Board schematics are not available, but the regulator voltages
found in /sys/kernel/debug/regulator/regulator_summary match those in
meson8m2-mxiii-plus.dts:

 DCDC1               0    0      0 unknown  1100mV     0mA     0mV     0mV
 DCDC2               0    0      0 unknown  1150mV     0mA     0mV     0mV
 DCDC3               0    0      0 unknown  1500mV     0mA     0mV     0mV
 LDO1                0    0      0 unknown  2900mV     0mA     0mV     0mV
 LDO2                0    0      0 unknown  1800mV     0mA     0mV     0mV
 LDO3                0    0      0 unknown  1800mV     0mA     0mV     0mV
 LDO4                0    0      0 unknown  2850mV     0mA     0mV     0mV
 LDO5                0    0      0 unknown  1800mV     0mA     0mV     0mV
 LDORTC1             0    0      0 unknown  2700mV     0mA     0mV     0mV
 LDORTC2             0    0      0 unknown   900mV     0mA     0mV     0mV

This patch takes the following approach:

 - Copy RN5T618 regulator nodes from meson8m2-mxiii-plus.dts
 - Remove some of the regulator names, which do not seem to apply
 - Verify regulator supply relations by starting without any relations
   (and without regulator-always-on) and seeing what breaks when the
   kernel turns off "unused" regulators.

This results in the following observations:

 - When LDO1 is turned off, the board resets
 - When DCDC1, DCDC2, DCDC3, LDO2, or LDO5 are turned off, the board (as
   observed through the serial port) stops running, so these must stay on
   at all times.
 - LDO4 (VCC2V8) appears to be unused on this board.
 - LDO3 (VCC1V8_USB) must stay on in order for USB to work, both the
   external USB ports and the internal USB wifi module.

The cpu-supply and mali-supply relations are also copied from
meson8m2-mxiii-plus.dts

Signed-off-by: J. Neuschäfer <j.ne@posteo.net>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20250428-fernsehfee-v2-4-293b98a43a91@posteo.net
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>