Bluetooth: hci_intel: Replace spinlock with mutex

Replace the device_intel list spinlock with a mutex.
devm_request_threaded_irq is not atomic and upcomming PM support should
be simpler.

Signed-off-by: Loic Poulain <loic.poulain@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>