Bug - PCFX not displaying 7MHz mode same as real console

[dshadoff]

The 7MHz dotclock (used by the HuC6270) does work, but Mednafen ignores it with certain timings (even values which my composite monitor & actual machine accepts).

(Tested using liberis examples)
Normally, the settings for a 5MHz dotclock would be something like what is used in the liberis examples:
eris_low_sup_set_video_mode(0, 2, 2, 4, 0x1F, 0x11, 2, 239, 2);

These should be changed when a 7MHz dotclock is used to something more like:
eris_low_sup_set_video_mode(0, 3, 3, 6, 0x2B, 0x11, 2, 239, 2);

Mednafen will display properly with the modified settings; however, it's not clear what the threshold of operation is.