Rather than have a twisty maze of special case allocations, move
instead to a data driven allocation. This should be the most robust
way to cope with the resource problems that the multiplicity of ways
of encoding 5 registers that have the misfortune of not being a power
of 2 nor contiguous.
Also, make it less impossible that pccard will work. I've not been able
to get my libretto floppy working, but it now fails later than before.
phk and I had similar ideas on this during the 5.3 release cycle, but
it wasn't until recently that I could test more than one allocation
scenario.
MFC After: 1 month (5.4 if possible, 5.5 if not)
65cbf19ef7