Bluetooth: Add offload feature under experimental flag

Allow user level process to enable / disable codec offload
feature through mgmt interface. By default offload codec feature
is disabled.

Signed-off-by: Kiran K <kiran.k@intel.com>
Reviewed-by: Chethan T N <chethan.tumkur.narayan@intel.com>
Reviewed-by: Srivatsa Ravishankar <ravishankar.srivatsa@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>