NFC: Add NCI multiple targets support

Add the ability to select between multiple targets in NCI.
If only one target is found, it will be auto-activated.
If more than one target is found, then DISCOVER_NTF will be
generated for each target, and the host should select one by
calling DISCOVER_SELECT_CMD. Then, the target will be activated.
If the activation fails, GENERIC_ERROR_NTF is generated.

Signed-off-by: Ilan Elias <ilane@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>