drm/amd/display: Remove duplicate interface for programming FB

[Why]
There are currently two interfaces for exactly the same thing:
hupb_update_dchub in hupb and update_dchub in hubbub. The hubbub
version is currently unused past dcn10, largely because the call
from the dcn10 hardware sequencer does not call through the
interface, so the hupb interface was used instead. This is
confusing because of the duplicate code, the unused functions,
and the fact that more that one block currently owns this set
of registers.

[How]
Remove the hubp interface entirely, as well as the register
declarations that are not longer needed because of this. Change
the call site to always call the hubbub version through the
interface. Fix the update_dchub function in dcn20_hubbub.c to
program the correct registers for dcn20.

Signed-off-by: Julian Parkin <julian.parkin@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>