Bluetooth: btnxpuart: implement powerup sequence

NXP bluetooth chip shares power supply and reset gpio with a WLAN
chip. Add support for power supply and reset and enforce powerup
sequence:
- apply power supply
- deassert reset/powerdown

Signed-off-by: Catalin Popescu <catalin.popescu@leica-geosystems.com>
Reviewed-by: Neeraj Sanjay Kale <neeraj.sanjaykale@nxp.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>