Bluetooth: btnxpuart: Add system suspend and resume handlers

This adds handling for system suspend and resume. While the host enters
suspend state, the driver will drive the chip into low power state.

Similarly when system is resuming, the driver will wake up the chip.

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