Revert of ozone: Remove the "drm" software composited platform

Revert of ozone: Remove the "drm" software composited platform (patchset #2 id:20001 of https://codereview.chromium.org/1345703002/ )

Reason for revert:
Broke chrome-sdk builds until it updates.

Original issue's description:
> ozone: Remove the "drm" software composited platform
> 
> This is a software-only platform that was used early in the process
> of bringing up the Chrome OS ozone/freon (no X11) build. It's time to
> remove it because it now requires not only scary flags to get it going,
> but also a patch (https://codereview.chromium.org/1216303004/).
> 
> If we need a build with software rasterization let's use vgem+swrast like
> our VMtests do.
> 
> BUG=531814
> TEST=link still works fine with platform=gbm
> 
> Committed: https://crrev.com/d0620b8a4b025b5d808644068d155e07dcaa0276
> Cr-Commit-Position: refs/heads/master@{#349012}

TBR=dnicoara@chromium.org,alexst@chromium.org,agrieve@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=531814

[spang, 2015-09-15 23:40:22]

Created Revert of ozone: Remove the "drm" software composited platform

[spang, 2015-09-15 23:58:28]

The CQ bit was unchecked by spang@chromium.org