rockchip: rk3399-puma: Cleanup of vdd_log DTS entry.

rockchip: rk3399-puma: Cleanup of vdd_log DTS entry.

This patch eliminates the non-standard entries "rockchip,pwm_id"
and "rockchip,pwm_voltage". They are neither documented nor
read out by any driver.

Additionally it introduces the entry regulator-init-microvolt
and sets it to 900 mV, which is the default target value
for VDD_LOG.

Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>