power: supply: axp20x_usb_power: Make VBUS and IIO config per device

Make reading of the vbus value and configuring of the iio channels
device specific, to allow additional devices (such as the AXP717) to
be supported by this driver.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240821215456.962564-5-macroalpha82@gmail.com


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>