drm/amdgpu: fix reboot failure issue for virtualization

Reboot process will call HW fini functions of IP blocks. For virt,
need to send event three before hw fini and send event four after
hw fini.

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