Hearing Aid: set BLE phy to 2M if local and peer indicate PHY 2M support

Set the BLE phy to 2M if the BT controller and peer Hearing Aid device
indicate phy 2M support, otherwise, use default phy channel.

Bug: 135769508
Test: 1.Forget/Repair Hearing Aid device check whether phy is expected.
2.Disconnect/Reconnect Hearing Aid device check whether phy is expected.
3.HearingAid device power off/on, check whether phy is expected.

Change-Id: Ib410a8885f3a68c361bb97d5c9a3833f2a1be528