x86: fold special-operand insn attributes into a single enum

x86: fold special-operand insn attributes into a single enum

Attributes which aren't used together in any single insn template can be
converted from individual booleans to a single enum, as was done for a few
other attributes before. This is more space efficient. Collect together
all attributes which express special operand constraints (and which fit
the criteria for folding).