hdmirx: optimize for audio fifo [1/1]

hdmirx: optimize for audio fifo [1/1]

PD#SWPL-2114

Problem:
When change audio channel count on VG-877, the subpkts of skipped
middle channels are still carried, thus causing afifo overflow

Solution:
When afifo overflow, then store all audio subpkts(8ch)
into afifo, and output 8ch audio from afifo

Verify:
R321

Change-Id: I4b0933935d3a1aed20be10a7a8d3fe23c3a39323
Signed-off-by: Hang Cheng <hang.cheng@amlogic.com>