Bluetooth: btnxpuart: Add support for IW624 chipset

This adds support for NXP IW624 chipset in btnxpuart driver
by adding FW name and bootloader signature. Based on the
loader version bits 7:6 of the bootloader signature, the
driver can choose between selecting secure and non-secure
FW files.
For cmd5 payload during FW download, this chip has addresses
of few registers offset by 1, so added boot_reg_offset to
handle the chip specific offset.

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