dt-bindings: net: bluetooth: nxp: Add support for power save feature using GPIO

This adds a new optional device tree property device-wakeup-gpios, which
specifies the GPIO connected to BT_WAKE_IN pin of the NXP chipset.

If this property is defined, the driver will use this GPIO for driving chip
into sleep/wakeup state, else use the UART break signal by default.

Signed-off-by: Neeraj Sanjay Kale <neeraj.sanjaykale@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>