mb/google/brox/lotso: Enable BT audio offload config

mb/google/brox/lotso: Enable BT audio offload config

Enable BT audio offload of WIFI_CNVI_WIFI6E or unprovisioned
based on fw_config.

BUG=b:373510270
TEST=Build and boot to Lotso. Verify the config from serial logs.

w/o this CL -
```
[SPEW ]  -- CNVi Config --
[SPEW ]  CNVi Mode= 1
[SPEW ]  Wi-Fi Core= 1
[SPEW ]  BT Core= 1
[SPEW ]  BT Audio Offload= 0
```

w/ this CL -
```
[SPEW ]  -- CNVi Config --
[SPEW ]  CNVi Mode= 1
[SPEW ]  Wi-Fi Core= 1
[SPEW ]  BT Core= 1
[SPEW ]  BT Audio Offload= 1
```

Signed-off-by: Wentao Qin <qinwentao@huaqin.corp-partner.google.com>
Change-Id: I36f8c3fb24166c86d5fc4099fa9cde8cdecb9d49
Reviewed-on: https://review.coreboot.org/c/coreboot/+/84768
Reviewed-by: Bob Moragues <moragues@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jian Tong <tongjian@huaqin.corp-partner.google.com>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>