clock: esp32c6: enable and calibrate digital regulators

Enable the RTC-domain and main digital regulators early in clock init,
then load and program the factory/runtime calibrated bias values for
high-power and low-power regulators into the PMU. This ensures the
correct voltage/current settings for stable, low-noise clock operation
in active, modem and sleep modes.

Signed-off-by: Sylvio Alves <sylvio.alves@espressif.com>