Fix eARC TX retransmission issue in HDMI CTS

[Description]
HDMI CTS - HFR-5-1-63 eARC TX Retransmits Basic Audio failed due to
improper system audio mode handling.

[Root Cause]
System audio mode was not correctly set when AVR device info was
unavailable, causing eARC TX retransmission failure.

[Solution]
Add checks for eARC to set system audio mode.

[Test Report]
Verify HFR5-1-63 PASS.

Flag: EXEMPT bugfix
Bug: 400616469
Change-Id: I6a606b37009e4161c0a3812b13ef0a9772345b68