Bluetooth: Audio: fix BIS_Sync_State for BASS server

BASS server need to notify that both BIS and PA are no longer synced by
setting all required fields to 0 after client stops BIS by sending a
BIG control PDU with a BIG TERMINATED indication.

meanwhile BIG_Encryption in the notification should also be reset to be
BT_BAP_BIG_ENC_STATE_NO_ENC when BIS is not synced anymore.

Signed-off-by: Ping Wang <pinw@demant.com>