Add support for PL2303HXN to uplcom(4).
Code changes in this commit were obtained from straight from OpenBSD's
uplcom.c with almost no modification, the list of chip names and USB
IDs was obtained from Linux.
Differential Revision: https://reviews.freebsd.org/D27952
Submitted by: tomli_tomli.me (Yifeng Li)
Sponsored by: Mellanox Technologies // NVIDIA Networking
Git Hash: 2e0dd1574137757c4267c38c11493aab005136e3
Git Author: hselasky@FreeBSD.org