linuxkpi: Move <linux/vga.h> out of dummy/ and define some constants

[dumbbell]

Summary

Why

This header as well as the defined constants are now used by the i915 DRM driver in Linux 5.18.

This is part of the update of the DRM drivers to Linux 5.18.

[emaste]

What do we typically do for header/copyright statements in these sorts of files?

[manu]

Duplicate of https://reviews.freebsd.org/D42793 ?

[dumbbell]

Address the license issue reported by @emaste.

[dumbbell]

In D43013#981046, @manu wrote:

Duplicate of https://reviews.freebsd.org/D42793 ?

I confirm it is.

[emaste]

vga.h added in 5e6bddfc43300f344d44afdc80f1bb7a37bd84fc