[Why]
Change DCN10 hubbub to use hubbub as a base and allow all future DCN
hubbubs to do the same instead of using DCN10_hubbub. This increases
readability and doesn't require future hubbubs to inherit anything
other than the base hubbub struct.

[How]
Create separate DCN10_hubbub struct which uses the hubbub struct as
a base.
Signed-off-by: Eryk Brol <eryk.brol@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>