regulator: tps6594-regulator: Add driver for TI TPS6594 regulators

This patch adds support for TPS6594 regulators (bucks and LDOs).
The output voltages are configurable and are meant to supply power
to the main processor and other components.
Bucks can be used in single or multiphase mode, depending on PMIC
part number.

Signed-off-by: Jerome Neanne <jneanne@baylibre.com>
Signed-off-by: Esteban Blanc <eblanc@baylibre.com>
Link: https://lore.kernel.org/r/20230522163115.2592883-4-eblanc@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>