regulator: mp8859: Implement set_current_limit()

The mp8859 implements support for current limiting, provide support for
configuring this via the driver. The datasheet recommends that if the
device has hit the current limit then any changes should be implemented
via a ramp so we do so in the driver.

Tested-by: Markus Reichl <m.reichl@fivetechno.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://msgid.link/r/20240225-regulator-mp8859-v1-8-68ee2c839ded@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>