Redesign HFP Client call handling

1. Use UUIDs to interact between the upper layers and state machine.
2. Centralized place for managing calls.
3. Mechanism to co-relate outgoing calls with the AT+CLCC reply
4. Get rid of non-ECC hacks (we basically do not support devices not
supporting ECC)

Bug: b/29788044
Change-Id: I497c59583124825fad9be800a7c0a53920e67d4c
(cherry picked from commit 05462fe4)