regulator: mp8859: Support status and error readback

The MP8859 can report if it is in regulation and detect over temperature
conditions, report this information via the relevant regulator API
calls.

Tested-by: Markus Reichl <m.reichl@fivetechno.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://msgid.link/r/20240225-regulator-mp8859-v1-6-68ee2c839ded@kernel.org


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