Bluetooth: btnxpuart: Implement host-wakeup feature

This implements host wakeup feature by reading the device tree property
wakeup-source and 'wakeup' interrupt, and nxp,wakeout-pin, and configuring
it as a FALLING EDGE triggered interrupt.

When host is suspended, a trigger from the WAKE_OUT pin of the
controller wakes it up.

To enable this feature, both device tree properties are needed to be
defined.

Signed-off-by: Neeraj Sanjay Kale <neeraj.sanjaykale@nxp.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>