drm/amdkfd: Optimize out sdma doorbell array in kgd2kfd_shared_resources

We can directly calculate sdma doorbell indexes in the process doorbell
pages through the doorbell_index structure in amdgpu_device, so no need
to cache them in kgd2kfd_shared_resources any more. This alleviates the
adaptation needs when new SDMA configurations are introduced.

Signed-off-by: Yong Zhao <Yong.Zhao@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>