audio: add stream mute and continuous clk [1/1]

audio: add stream mute and continuous clk [1/1]

PD#SWPL-2952

Problem:
Pop noise could be heard
when switching between sources.

Solution:
1. Add stream digital mute functions.
2. continuous clock to eliminate
  the clk reset issue.

Verify:
Local verified.

Change-Id: I372f4c03aaf875d75aa903c9c2dfda00619af000
Signed-off-by: Shuai Li <shuai.li@amlogic.com>