regulator: isl9305: Add Intersil ISL9305/H driver

The ISL9305 and ISL9305H are mini-PMICs offering two DCDC regulators and
two LDO regulators. While there are some register differences between them
these do not affect the current Linux driver as the relevant features are
not yet supported.

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