drm/amdgpu: allocate doorbell index for multi-die case

Allocate different doorbell index for kiq/kcq rings
on each die

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>