drm/amdgpu: dump job ibs in the devcoredump

drm/amdgpu: dump job ibs in the devcoredump

Now that we have a worker thread, we can try to access the
IBs of the job. The process is:
* get the VM from the PASID
* get the BO from its VA and the VM
* map the BO for CPU access
* copy everything, then add it to the dump
Each step can fail so we have to be cautious.
These operations can be slow so when amdgpu_devcoredump_format
is called only to determine the size of the buffer we skip all
of them and assume they will succeed.

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v3: use kvfree
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Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>