[Coco] Patching NitrOS9 for 8 meg

[RETRO Innovations]

     On May 3, 2018 at 1:51 PM Dave Philipsen <[1]dave at davebiz.com>
     wrote:
     That’s interesting. So there are 32 task registers in the MMU of the
     CoCoMem, right? Are they extended out from the original two at
     $FFA0-FFAF? How do the new registers map into the I/O space?

   There are only 16 spots in the register map to contain things, :-)
   Obviously, the code is not final as yet, so changes can be made, but as
   I was finishing CoCoMEM Jr, I came up with a nice plan.

   The 16 byte space in register mappings becomes a "window" into the MMU
   space.  When you flip a few bits, you get 8 "words" of MMU data in
   $ffa0-$ffaf, corresponding to MMU blocks 0-7.  words are
   highbyte:lowbyte, so LDD and such can be used.

   Not all bits are straight MMU bits.  The top 3 bits of the MMU word are
   currently reserved, and are designed for:

   bit 15: write protected block

   bit 14: INT on write

   bit 13: reserved

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