regulator: Add support for TPS6286x

TI's TPS62864/TPS6286/TPS62868/TPS62869 are high-frequency synchronous
step-down converters controlled via I2C.  There are differences in the
electrical characteristics and packaging between the variants, but the
register interfaces are identical.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20220204155241.576342-3-vincent.whitchurch@axis.com


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