Turn drm2 back on in TEGRA124

[imp]

Summary

After much discussion, re-import the old drm2 base code (but not the
intel or radeon drivers) as a transition aide for TEGRA124. To make it
clear this is only for TEGRA, it's moving (without history) to
sys/arm/nvidia/drm2/dev/drm2. This will restore the status quo for the
TEGRA port so that it isn't broken just before 12.0 is branched.

However, this should be viewed as a stop-gap measure. Future graphics
support should be done via the new graphics group working to shim
drm-next into FreeBSD. All vestiges of drm2 support will be removed
in the run up to FreeBSD 13 release, or sooner if there's an suitable
solution for this platform available.

Approved by: mmacy@, mmel@, core@

Note: My plan for the actual repo commit is to svn cp sys/dev/drm2@338168 sys/arm/nvidia/drm2/dev/drm2 followed by a svn rm of the stuff not needed then apply the build patches, then do a commit so we have a nice, atomic bundle.

also, sys/arm/dev/drm2 is fine too if mmel thinks this will be used outside of tegra.

Test Plan

I have no ability to test this, but it compiles.

[imp]

There's three files that matter here, given my plan: sys/conf/Makefile.arm, sys/arm/conf/TEGRA124 and sys/arm/nvidia/tegra124/files.tegra124
The rest are just copies from dev/drm2 before the rm.

[mmacy]

LGTM

[rgrimes]

I respectfully request that a straight revert of the commits be done rather than this, for one this does not allow us to do the proper deprecation commits, nor to merge those commits back to stable/11. This is still a major violation of deprecation policy. Warner, would you new policy allow this type of thing to be accepted? I would hope not.

Furthermore this differential is failing build, something we do not want hours before code freeze!

[kevans]

In D16870#359353, @rgrimes wrote:

Furthermore this differential is failing build, something we do not want hours before code freeze!

Are you basing that on actually having downloaded the diff and built it, or are you basing that on Harbormaster pointing out spelling mistakes? https://reviews.freebsd.org/B19101 -- because if it's the latter, Harbormaster doesn't actually build things.

[imp]

In D16870#359353, @rgrimes wrote:

I respectfully request that a straight revert of the commits be done rather than this, for one this does not allow us to do the proper deprecation commits, nor to merge those commits back to stable/11. This is still a major violation of deprecation policy. Warner, would you new policy allow this type of thing to be accepted? I would hope not.

Furthermore this differential is failing build, something we do not want hours before code freeze!

It builds. I've built it 4 differnet times.

[imp]

this was resolved.