Bluetooth: Add initial support for BR/EDR discovery

This allows to start (general or limited) BR/EDR discovery. Inquiry
is active until explicitly disabled by application. This is to keep
BR/EDR discovery API similar to LE scan API.

< HCI Command: Inquiry (0x01|0x0001) plen 5
        Access code: 0x9e8b33 (General Inquiry)
        Length: 61.44s (0x30)
        Num responses: 0
> HCI Event: Command Status (0x0f) plen 4
      Inquiry (0x01|0x0001) ncmd 1
        Status: Success (0x00)
> HCI Event: Inquiry Complete (0x01) plen 1
        Status: Success (0x00)

Change-Id: I946fbd881e6d0460be28a9975acd564ae32896e8
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>