Polishing of isa_parser.py internal operand handling, resulting in

Polishing of isa_parser.py internal operand handling, resulting in
minor change to syntax of 'def operands' in ISA descriptions.

arch/alpha/isa/main.isa:
arch/mips/isa/operands.isa:
arch/sparc/isa/operands.isa:
    Change 'def operands' statement to work with new
    isa_parser changes.
arch/isa_parser.py:
    Merge OperandTraits and OperandDescriptor objects into a
    unified hierarchy of Operand objects.
    Required a change in the syntax of the 'def operands'
    statement in the ISA description.

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extra : convert_revision : cb43f1607311497ead88ba13953d410ab5bc6a37