bluez5: HW offload SCO support

For offload SCO, the audio stream should be routed to/from Bluetooth chipset via ALSA.
To do this, this commit prevent the creation of the sco-source or sco-sink nodes, and replace them by loopback nodes.
It's up to the platform to correctly set the route to the Bluetooth chipset ALSA entries.

When the loopback node state change to running, the script also call the bluetoothOffloadActive param of the device to start/stop the SCO link.

This also adds a sample script for PinePhone which selects the correct audio routes when the SCO offload loopback nodes are running.