128k on GX-4000

Disclaimer: Adding ram to the GX-4000 is mostly useless. The only reason I did this is for fun...

1) Get two CPC-Plus compatible ram.

I used KM41464AP-12, but there are other chips of the same kind that should work.

2) Solder them both piggy back on the existing ram chips, except for the NCAS signal (pin 16)

Leg 16 is used by the ASIC to select the RAM bank to use. All other signals are totally parallel.