regulator: aw37503: add regulator driver for Awinic AW37503

Add regulator driver for the device Awinic AW37503 which is single
inductor - dual output power supply device. AW37503 device is
designed to support general positive/negative driven applications
like TFT display panels.

AW37503 regulator driver supports to enable/disable and set voltage
on its output.

Signed-off-by: Alec Li <like@awinic.com>
Link: https://lore.kernel.org/r/20230821035355.1269976-2-like@awinic.com


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