Bluetooth: Add support for PIN code handling in the management interface

This patch adds the necessary commands and events needed to communicate
PIN code related actions between the kernel and userspace. This includes
a pin_code_request event as well as pin_code_reply and
pin_code_negative_reply commands.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>