drm/amdgpu: Present amdgpu_task_info in VM_FAULTS.

Extract and present the reposnsible process and thread when
VM_FAULT happens.

v2: Use getter and setter functions.

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>