drivers: Narrow Band Unit interruption driver creation

Creation of the new zephyr\soc\nxp\common\nxp_nbu.c driver which manage
the interruption of the NBU. This modification is mandatory to support a
coex application which includes Bluetooth and 802.15.4 on the same
narrow band path.

Signed-off-by: Xavier Razavet <xavier.razavet@nxp.com>