Support other sizes of charsets in the HELP menu

[HovKlan-DH]

To my knowledge then only 16x16 charsets are supported, but it would be nice with alternative sizes (e.g. 12x12).

This is just wishful thinking from my side, and naturally not very important :-) Nice-to-have feature.

I am MegaBeauvais#9623 on MEGA65 Discord.

[sy2002]

@HovKlan-DH / MegaBeauvais: Thank you for this enhancement request. This feature would need some refactoring here:

https://github.com/sy2002/MiSTer2MEGA65/blob/master/M2M/vhdl/av_pipeline/vga_osm.vhd#L87

Right now we have other priorities but I leave this enhancement request open for the future.

[MJoergen]

A step in this direction has been done in commit 4c3a6e3