[Coco] SAMx8: Dragon 64 512K expansion

[Ciaran Anscomb]

Take a SAMx4.

Stick some SRAM next to it.

Strip out anything to do with DRAM.

What can still fit in the CPLD?

Website here: https://www.6809.org.uk/dragon/samx8/
with manual here: https://www.6809.org.uk/dragon/samx8/doc/samx8.pdf

The page mapping is course, but I'm thinking that having the COMMON
flag register fix the top 8K in place, it may just be a reasonable fit
for Fuzix.

With apologies that it's probably not very directly relevant here as it's
very much designed to plug into TWO sockets on a Dragon 64 motherboard -
even the Tano layout differs...

..ciaran