ASoC: aw8896: add aw8896 SmartPA driver

This is the initial driver for SmartPA aw8896.
This driver registers an i2c client to access codec register.
The driver acts as the codec driver in ASoC model, it registers
dai driver and widigets to control the behavior the codec and
provides some other methods like firmware loading.

Change-Id: Ifb9578702110bd2ad466556e86bf7eb1eb1ad10e
Signed-off-by: Nick Li <liweilei@awinic.com.cn>
Git-commit: 2f0896eb28cdeb2d87e9e4749998c4beb4b26d63
Git-repo: https://github.com/awinic-driver/aw8896.git


[lixiao@codeaurora.org: trivial changes as per kernel coding style]
Signed-off-by: Xiao Li <lixiao@codeaurora.org>