drm/amdgpu Moving amdgpu asic types to a separate file

Amdgpu asic types will be required for other drivers too.
Hence, its better to keep it in a separate include file.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Akshu Agrawal <akshu.agrawal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>