Extend the existing fan53555 driver to support the Rockchip RK860X
regulators.

RK8600/RK8601 are pretty similar to the FAN53555 regulators.

RK8602/RK8603 are a bit different, having a wider output voltage
selection range, from 0.5 V to 1.5 V in 6.25 mV steps. They also use
additional VSEL0/VSEL1 registers for the voltage selector, but the
enable and mode bits are still located in the original FAN53555 specific
VSEL0/VSEL1 registers.
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230406194158.963352-9-cristian.ciocaltea@collabora.comSigned-off-by: Mark Brown <broonie@kernel.org>