drm/amdgpu: update vmc interrupt routine to support 3 vmhubs

There is one more vmc interrupt and mmhub on Arcturus.

Signed-off-by: Le Ma <le.ma@amd.com>
Acked-by: Snow Zhang &lt; <Snow.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>