ASoC: aw8896: add logic to handle regulator for DVDD

aw8896's DVDD is not powered by default, add logic to read regulator info
from device tree, and enable power for DVDD in the driver probe function.

Change-Id: I544ef3e8e7f273f868cefc6a3ff27b6e7f9ed768
Signed-off-by: Xiao Li <lixiao@codeaurora.org>