Add YMZ custom cart support

[Pegmode]

Add support for Iyatemu's custom YMZ PSG Game Boy cart. (YMZ284 or YMZ294)

https://twitter.com/iyatemu/status/882337872568885248

tl;dr if the YM addresses are $6400 and $6401 for an MBC5 ROM, literally no other work has to be done, you just write to it as normal (every other mapper uses that area for some type of ROM or RAM bank selection)

[Pegmode]

Info:
$6400 is a 4-bit value for address, $6401 is the data for that address

extra:
/CS and /WR are tied together, (minimum delay of 0ns is specified in the timing specs) So selecting 6400 pulls both low driving A0 selects whether it's in Data or Address input mode then it's just a matter of writing stuff 6400, write $08 6401, write $0C Sets the volume of Channel A to $0C same for $08, 09, 0A

Registers + wr from datasheet:
6400, $07 - Channel Mixer 6401, $16 - bXX001000 (noise mode channel A) 6400, $06 - noise frequency 6401, $14 6400, 08 - CH A amplitude 6401, $0C