regulator: tps6586x: Prepare supporting fixed regulators
regulator: tps6586x: Prepare supporting fixed regulators

Add the required definitions and macros to allow easily adding fixed
regulators. This required for the TPS658640 that doesn't allow setting
the LDO_RTC output voltage.

Signed-off-by: Alban Bedel <825cb1d71292b66c34fe6b2f34d0838d6f1a9969@avionic-design.de>
Signed-off-by: Mark Brown <b51b9a92386687a9ac927cebfa0f978adeb8cea5@linaro.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs