Bluetooth: Add initialization tracking to HCI Three-wire driver

This patch adds tracking for the uninitialized, initialized and active
states for Three-wire UART. This is needed so we can handle periodic
sending of the Link Establishment messages before reaching active state
and so that we do not try to do any higher level HCI data transmission
before reaching active state.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>