drm/amdgpu: specify sdma instance 5~7 with second mmhub type

On Arcturus, sdma instance 5~7 is connected to the second mmhub. The vmhub type
in amdgpu_ring_funcs is constant, so we create an individual amdgpu_ring_funcs
with different vmhub type(AMDGPU_MMHUB_1) for these sdma instances.

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>