Bluetooth: btnxpuart: Rename IW615 to IW610

This changes the chip name of IW615 to IW610.

IW610 (formerly called IW615) is yet to be released to broad market,
hence there is no issue of backward compatibility.

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