floss: Add sysprops handler and set default values

A recent sysprops refactor changed the default value of a sysprop from
true to false and this caused a legacy AVRCP path to be taken which is
not well tested.

Update the sysprops code with a new branch for TARGET_FLOSS and set the
default value for avrcp target to True.

Bug: 230474915
Tag: #floss
Test: ChromeOS automated tests

Change-Id: Ifea8b071c6dbffb2978a5139ea7b304082d2cf34