Get bluetooth working on MBP13,3

[roadrunner2]

The main two issues were the timing out of operations due to wrong baudrate (2nd commit) and not finding the UART (3rd commit). Things work reasonably well with this, though I still occasionally see a timeout on the first command, necessitating a re-attach of the tty.

I still see the following error when attaching the tty:

 Bluetooth: hci0: BCM: failed to write update baudrate (-16)   (-EBUSY)

But it is benign, as the UART device does not appear to need its baud rate changed.

Finally, the 4th commit fixes the following two BUG's:

 BUG: sleeping function called from invalid context at kernel/locking/mutex.c
 in_atomic(): 1, irqs_disabled(): 0, pid: 7303, name: kworker/7:3
 INFO: lockdep is turned off.
 CPU: 7 PID: 7303 Comm: kworker/7:3 Tainted: G        W  OE   4.13.2+ #17
 Hardware name: Apple Inc. MacBookPro13,3/Mac-A5C67F76ED83108C, BIOS MBP133.8
 Workqueue: events hci_uart_write_work [hci_uart]
 Call Trace:
  dump_stack+0x8e/0xd6
  ___might_sleep+0x164/0x250
  __might_sleep+0x4a/0x80
  __mutex_lock+0x59/0xa00
  ? lock_acquire+0xa3/0x1f0
  ? lock_acquire+0xa3/0x1f0
  ? hci_uart_write_work+0xd3/0x160 [hci_uart]
  mutex_lock_nested+0x1b/0x20
  ? mutex_lock_nested+0x1b/0x20
  bcm_dequeue+0x21/0xc0 [hci_uart]
  hci_uart_write_work+0xe6/0x160 [hci_uart]
  process_one_work+0x253/0x6a0
  worker_thread+0x4d/0x3b0
  kthread+0x133/0x150
  ? process_one_work+0x6a0/0x6a0
  ? kthread_create_on_node+0x70/0x70
  ret_from_fork+0x2a/0x40

---

 BUG: sleeping function called from invalid context at kernel/locking/mutex.c
 in_atomic(): 1, irqs_disabled(): 0, pid: 13796, name: kworker/u16:2
 INFO: lockdep is turned off.
 CPU: 1 PID: 13796 Comm: kworker/u16:2 Tainted: G        W  OE   4.13.2+ #17
 Hardware name: Apple Inc. MacBookPro13,3/Mac-A5C67F76ED83108C, BIOS MBP133.8
 Workqueue: events_unbound flush_to_ldisc
 Call Trace:
  dump_stack+0x8e/0xd6
  ___might_sleep+0x164/0x250
  __might_sleep+0x4a/0x80
  __mutex_lock+0x59/0xa00
  ? trace_hardirqs_on+0xd/0x10
  ? hci_recv_frame+0x68/0xa0 [bluetooth]
  ? h4_recv_buf+0x17a/0x2f0 [hci_uart]
  mutex_lock_nested+0x1b/0x20
  ? mutex_lock_nested+0x1b/0x20
  bcm_recv+0x73/0x130 [hci_uart]
  hci_uart_tty_receive+0x61/0xa0 [hci_uart]
  tty_ldisc_receive_buf+0x48/0x50
  tty_port_default_receive_buf+0x49/0x70
  flush_to_ldisc+0x83/0xa0
  process_one_work+0x253/0x6a0
  worker_thread+0x4d/0x3b0
  kthread+0x133/0x150
  ? process_one_work+0x6a0/0x6a0
  ? kthread_create_on_node+0x70/0x70
  ret_from_fork+0x2a/0x40