power: supply: core: Avoid duplicate hwmon device from thermal framework

When the power supply device being registered supports a temperature
readout, the core registers a thermal zone for it. The thermal core
would register a hwmon device for that unless told otherwise.

When CONFIG_POWER_SUPPLY_HWMON is enabled, the power supply core creates
a hwmon device. This results in a second entry, one which has a better
name than the one registered through the thermal framework. It could
potentially have readouts other than temperature.

To simplify the result, tell the thermal framework to not register a
hwmon device if CONFIG_POWER_SUPPLY_HWMON is enabled. The result is
one hwmon device with all the readings the device supports.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>