platform/chrome: cros_ec: Add command for regulator control.

Add host commands for voltage regulator control through ChromeOS EC.

Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20200612040526.192878-3-pihsun@chromium.org


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