nrf52_bsim: Add header to allow reusing native_posix drivers

This board and the native_posix board share the POSIX architecture.
Some of the native_posix drivers/backends only rely on the
underlaying operating system API, and do not require any special
HW model to operate.
Therefore it is quite easy to reuse some of them into this board.

Currently the only limitation for some, is the interface they use
in the board to register their command line arguments.
This header provides a minimal shim to rename the, otherwise
equivalent, call.

Signed-off-by: Alberto Escolar Piedras <alpi@oticon.com>