Bluetooth: Add support for using the crypto subsystem

This will allow using the crypto subsystem for encrypting data. As SMP
(Security Manager Protocol) is implemented almost entirely on the host
side and the crypto module already implements the needed methods
(AES-128), it makes sense to use it.

There's now a new module option to enable/disable SMP support.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Signed-off-by: Anderson Briglia <anderson.briglia@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

net/bluetooth/Kconfig

@@ -22,6 +22,7 @@ menuconfig BT
 	     BNEP Module (Bluetooth Network Encapsulation Protocol)
 	     CMTP Module (CAPI Message Transport Protocol)
 	     HIDP Module (Human Interface Device Protocol)
+	     SMP Module (Security Manager Protocol)
 
 	  Say Y here to compile Bluetooth support into the kernel or say M to
 	  compile it as module (bluetooth).
@@ -36,11 +37,18 @@ if BT != n
 config BT_L2CAP
 	bool "L2CAP protocol support"
 	select CRC16
+	select CRYPTO
+	select CRYPTO_BLKCIPHER
+	select CRYPTO_AES
+	select CRYPTO_ECB
 	help
 	  L2CAP (Logical Link Control and Adaptation Protocol) provides
 	  connection oriented and connection-less data transport.  L2CAP
 	  support is required for most Bluetooth applications.
 
+	  Also included is support for SMP (Security Manager Protocol) which
+	  is the security layer on top of LE (Low Energy) links.
+
 config BT_SCO
 	bool "SCO links support"
 	help