Revert "Get rid of color_table_cache member as well"

This reverts commit 9c47003f41c55c0d3c5db31b8f8ce20510b35030.
Revert "Remove color_table_cache - SuperGrafx is its own core now"

This reverts commit 33589c86d190e38d87a7efa38cdcac09c2df3d5e.