MFC r329832, r329926

r329832:
[chvgpio] add GPIO driver for Intel Z8xxx SoC family

Add chvgpio(4) driver for Intel Z8xxx SoC family. This product
was formerly known as Cherry Trail but Linux and OpenBSD drivers
refer to it as Cherry View. This driver is derived from OpenBSD
one so the name is kept for alignment with another BSD system.

Submitted by: Tom Jones <tj@enoti.me>
Reviewed by: gonzo, wblock(man page)
Differential Revision: https://reviews.freebsd.org/D13086

r329926:
Add SPDX tags for chvgpio driver sources

Also move $FreeBSD$ keyword in header to BSD license