Git repository for new DRM

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

I've published my Git repository of porting Linux's DRM on Github at
<https://github.com/riastradh/netbsd-src>, which you can check out
using:

   git clone -b riastradh_drm2 git://github.com/riastradh/netbsd-src.git

This repository is a clone of Joerg Sonnenberger's Git mirror of src,
with three extra branches:

- riastradh_drm2, my working branch with sys/external/bsd/drm2 added
to house the drm2 code and shims to make the code from Linux live
outside its natural habitat;

- riastradh_drm2_base, the point in src at which I imported the drm2
code; and

- vendor/LINUX_DRM2, containing under sys/external/bsd/drm2/dist the
verbatim code from Linux that I'm working from (minus GPL code, though
that may eventually go under external/bsd/drm2 for kernel modules).

This is still very much a work in progress, and I may rebase the
riastradh_drm2 branch at any time or do arbitrarily horrible things to
it; it's fit for browsing but not much else.

Currently for expedience I am building drm2 as a module in
sys/modules/drm2, but eventually I will hook it up into the kernel
configuration in the usual way.

To make it easier to identify what I have changed in the imported
code, I haven't deleted any; I have only added `#ifdef __NetBSD__'
sections.  Most of these sections are not really NetBSD-specific so
much as rendered a little more portable, to improve the chance they
could be fed upstream later.

Let me know if you have any comments or questions!