BUG/Portions of the intro to Yuna 2 (Japanese) do not display due to oddities in video handling

[dshadoff]

This is believed to be a result of:

  - at the second rcr, sprites and bg are both disabled,
    forcibly blanking the remainder of the screen.
mednafen does not like having the lower bound of the crop set higher than
0xF2. this will result in the lower-bound crop triggering after the vsync
handler, which ends up disable bg for the entire screen.
this appears to just be an emulation bug, though.
using a lower value like 0xF0 instead will fix it regardless.

[dshadoff]

More detail can be found in this conversation:
HERE

[Turboxray]

Wrote a test demo. From recently tests, when the VDC exists vsync pulse with waiting state (whether VCE asserts vsync and ends it, or it expires), the display regs in CR for BG and Sprites are latched. And if BG=SPRITE=0, then the frame is disabled and in "burst mode" for the entire frame.

[dshadoff]

Integrated and tested

[dshadoff]

Relocating burst mode unfortunately from #50 had side effects; we should roll this back and try to find a solution without side effects.

[pceDev16]

#50 has been rolled back.

[dshadoff]

Validated against pull request #89