illumos gate

Now that updated DRM code (and supporting AGP code)
has all moved to https://github.com/illumos/gfx-drm/
we should remove the old code from illumos-gate.

This will require a "heads up" to any distro. builders
who might still need the old DRM code. I know the
OI/hipster distro. has already moved off of it.
Any other distros still need it? For how long?

Some have questioned "Why do this?"

The main reason for moving the DRM drivers was that we learned the
DRM drivers and the DRM library share an interface (the huge set of
ioctl calls) that essentially requires that driver and library to be
"tightly coupled". In order to keep that interface from being
frequently broken (as it often was before the driver moved) those two
components should be built from the same gate. We didn't want to
import libdrm into illumos gate, so moving the driver into a gate
shared with libdrm was the solution chosen.