drm/amdgpu: Add support for logging process info in amdgpu_vm.

Add process and thread names and pids and a function to extract
this info from relevant amdgpu_vm.

v2: Add documentation and fix identation.

v3: Add getter and setter functions for amdgpu_task_info.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Acked-by: Jim Qu <Jim.Qu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>