ASoC: wcd9306: Dynamically change the current on vdd_cx power rail

The codec needs 10mA peak current on the vdd_cx power rail. But
without any audio activity on the codec, this power rail can
be operational with only 2mA current. Set the current on the
power rail dynamically depending on presence of active audio
activity.

Change-Id: I984380bf7888314133d81bb88506d81bb322eb1a
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>