regulator: as3722: set enable time for SD0/1/6

Add an enable time of 600us for SD0/1/6 to ensure that we have
enough setup time for the power rail.

Signed-off-by: Vince Hsu <vinceh@nvidia.com>
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Mark Brown <broonie@linaro.org>