drm/amdgpu: add the accelerator pcie class

v2: add the base class id for accelerator (lijo)
v3: add the new pci class in amdgpu tree (hawking)

Signed-off-by: Shiwu Zhang <shiwu.zhang@amd.com>
Acked-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>