Bluetooth: has: Make HAS registration dynamic

This changes HAS registration to be dynamic and let's the
application set Hearing Aid Type and binaural features.

Often, devices are flashed with generic firmware with some
features stored post factory production, requiring
the settings to be moved from compile time to run-time.

This change will increase the RAM usage as the GATT
service is moved from ROM to RAM.

Signed-off-by: Lars Knudsen <larsgk@gmail.com>
Co-author: Soren Engquist <soren@engquist.dk>