The Custom1, Custom2, and Custom3 sections for each of these filter
definitions is simply the original 1024 entry table repeated 3 times.

Note that these MiSTer values are 4x what UltiSID expects, so they
are right shifted two positions in the VHDL for UltiSID.

The filter_dc_offsets.xlsx file contains DC offsets extracted from
the mixer and filter for various SID implementations.
