Bluetooth: AMP support enabled by module param, default disabled

AMP feature is decommitted from Android PL's. Make advertising and
support for the A2MP protocol depend on an L2CAP module parameter
and make the default state disabled.

Change-Id: Icb9827d2d4205818d6c3b49e7a53938666f769e8
Signed-off-by: Peter Krystad <pkrystad@codeaurora.org>