atv_demod: tm2: add audio gain and interrupt. [1/1]

atv_demod: tm2: add audio gain and interrupt. [1/1]

PD#SWPL-5661, PD#SWPL-5659

Problem:
1.add gain register to control the L and R channel audio gain.
2.add atv interrupt for signal lock and unlock.

Solution:
1.add gain register to control the L and R channel audio gain.
2.add atv interrupt for signal lock and unlock.

Verify:
verified by ab301 and ab311.

Change-Id: I8a7cbe538939dd9418e27165d4c83a8f473f119b
Signed-off-by: nengwen.chen <nengwen.chen@amlogic.com>