[Why&How]
DMUB subsystem was continuing to use compile time offset calculation for
register access. Switch this to runtime calculation to stay consistent
with rest of DC code.

To enable this, an additional interface init_reg_offsets() are added to
DMUB's hw_funcs struct. Asics with runtime register offset calculation
enabled shall populate this hook with a fn pointer that will invoke the
necessary macros to calculate the offset.
Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>