Bluetooth: Merge INQUIRY and LE_SCAN discovery states

This patch merges DISCOVERY_INQUIRY and DISCOVERY_LE_SCAN states
into a new state called DISCOVERY_FINDING.

From the discovery perspective, we are pretty much worried about
to know just if we are finding devices than what exactly phase of
"finding devices" (inquiry or LE scan) we are currently running.
Besides, to know if the controller is performing inquiry or LE scan
we should check HCI_INQUIRY or HCI_LE_SCAN bits in hdev flags.

Moreover, merging this two states will simplify the discovery state
machine and will keep interleaved discovery implementation simpler.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>