drm/amdgpu: increase max number of ip base instances to 8

For Arcturus, the number of IP base instances is 8.

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>