floss: Disable enhanced sco connection via sysprop

Add a new sysprop, "bluetooth.sco.disable_enhanced_connection", so that
we can disable it on controllers where we know this is broken but can't
fix the firmware.

Bug: 255202220
Tag: #floss
Test: Ran HFP tests with value set to true and false.
Change-Id: Ib12f09d80c26b65e66fe14de9181230520a90ffc