GPU lockup dumping

[j.glisse at gmail.com]

So here is improved patchset, where i splited ground work necessary
for the dumping into their own patch. The debugfs improvement could
probably be usefull to intel instead of having i915 have it's own
debugfs file stuff.

The lockup dumping public api have been move into radeon_drm.h

Stressing the fact again that dump are self contained ie they have
all the data needed to be replayed (vertex, indices, shader, texture,
...).

Would really like to get this into 3.5, the new API is pretty much
straightforward and userspace tools can easily be made to convert
it to other format. The change to the driver is self contained.

Cheers,
Jerome