drm/amdkfd: CRIU export BOs as prime dmabuf objects

KFD buffer objects do not associate a GEM handle with them so cannot
directly be used with libdrm to initiate a system dma (sDMA) operation
to speedup the checkpoint and restore operation so export them as dmabuf
objects and use with libdrm helper (amdgpu_bo_import) to further process
the sdma command submissions.

With sDMA, we see huge improvement in checkpoint and restore operations
compared to the generic pci based access via host data path.

Suggested-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Signed-off-by: David Yat Sin <david.yatsin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>