regulator: tps6586x: Add support for the TPS658640

The TPS658640 has a different set of output voltage for most LDO and
the RTC LDO isn't settable. This chip also report 2 different version
ID, as the datasheet doesn't list the possible values the second ID
has simply been named TPS658640v2.

Signed-off-by: Alban Bedel <alban.bedel@avionic-design.de>
Signed-off-by: Mark Brown <broonie@linaro.org>