Bluetooth: SMP: Add support for Signing Information over BR/EDR

This allows to handle CSRK distributed by remote device.

> ACL Data RX: Handle 11 flags 0x02 dlen 21
      BR/EDR SMP: Signing Information (0x0a) len 16
        Signature key: 32b6247f80dc172be6198649a6322532

Jira: ZEP-605

Change-Id: I01ca67e134d7d8068d0336567a3fa9b9fdafc001
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>