amdgpu: ratelimit on vm faults to avoid spaming console

[Alex Deucher]

On Sun, Nov 6, 2016 at 11:35 PM, Edward O'Callaghan
<funfunctor at folklore1984.net> wrote:
> These are rather minor however should help stop some folks
> machines grinding to a halt when a userspace application somehow
> gets the GPU into some horrible state causing the console to fill
> very quickly. Applies on top of master.

I'm generally ok with the idea.  My only concern would be if this
would adversely affect the radeon GPUVM debugging options in mesa and
piglit. Nicolai? Marek?

Alex