svp64.py: group 32-bit instructions into the table

svp64.py: group 32-bit instructions into the table

The pysvp64asm code became really dirty with the addition of new
instructions, it's almost impossible to keep track of it. Some
instructions were not converted at all, due to incorrect check (all but
setvl/svshape). Some had wrong operand names (fsins, fcoss used RT, RA
operands, and this does not follow the spec). Some instructions had no
SV support, despite the fact they should (fsins).

This all became barely maintainable. From now on, instructions are
grouped into a special table. Ideally we should generate this table
from fields.txt, but there's no time for writing yet another parser.