Bluetooth: Add BT_HS config option

Move A2MP Module under BT_HS config option and allow
the user have flexible option to choose the feature only
they need

a2mp_discover_amp() & a2mp_channel_create() are a2mp module
entry point for master and slave, and this is dynamic
invoked depends on the userspace or remote request, then
we defined their implementation depends on BT_HS config

Signed-off-by: Arron Wang <arron.wang@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>