regulator: add smb208 support

Smb208 regulators are used on some ipq806x soc.
Add support for it to make it avaiable on some routers
that use it.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: Adrian Panella <ianchi74@outlook.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200219163711.479-1-ansuelsmth@gmail.com


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