fix for CRTC mutex corruption

[Ilija Hadzic <ihadzic@research.bell-labs.com>]

The following patch series fixes the mutex corruption problem
due to bit-copying of drm_crtc structure that happens when
drm_crtc_helper_set_config function takes the error-recovery
path. The patch series is the alternative solution for the
patch that was proposed and NACK-ed two weeks ago [1].

The actual fix is implemented in patch #6; preceding
5 patches are necessary prerequisites.

A couple of my own remarks:

1) Someone (including myself) may be tempted to eliminate the
bit-copy for encoder and connector structures as well. I would, however,
prefer to leave that improvement for a different patch series.
The primary reason is that this patch series addresses an acute
(and serious) problem (mutex corruption), while doing the equivalent
rework for connector and encoder structure would be only for the sake
of improving the code quality.

2) The problem exists in old (stable@...) kernels and my original intention
(in the patch that was NACK-ed [1]) was to make the fix simple enough
to be eligible for stable@.... This patch series is now probably more complex
than what stable@... may be willing to accept. So the question in my mind
is what we should do with the old kernels.

3) This patch series does not include the fix for incidental finding
described in earlier discussions about this problem [2] because it's not
the part of the fix that this patch series is targeting, so I'd leave
it for later.

regards,

Ilija

[1] http://lists.freedesktop.org/archives/dri-devel/2013-October/047479.html
[2] http://lists.freedesktop.org/archives/dri-devel/2013-October/047557.html