posix: ioctl: use fdtable.h FIONBIO and FIONREAD definitions

Rather than defining FIONBIO and FIONREAD at the POSIX layer,
define them at the Zephyr layer, in the Zephyr namespace, and
make the POSIX layer a simple wrapper.

This facilitates having a common dependency between POSIX and
networking rather than a cyclic one.

Signed-off-by: Christopher Friedt <cfriedt@meta.com>