drm/amdgpu:cleanup virt related define

move virtual machine related structure to amdgpu_virt.h
easy for developer to maintain for virualization stuffs

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>