Bluetooth: Add debugfs switch for forcing SMP over BR/EDR

To make it possible to use LE SC functionality over BR/EDR with pre-4.1
controllers (that do not support BR/EDR SC links) it's useful to be able
to force LE SC operations even over a traditional SSP protected link.
This patch adds a debugfs switch to force a special debug flag which is
used to skip the checks for BR/EDR SC support.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>