mainly added minor support for the basic arithmetic operations (add, mult, shift)

mainly added minor support for the basic arithmetic operations (add, mult, shift)

arch/mips/isa/bitfields.def:
    Add comment, move definition up in file
arch/mips/isa/decoder.def:
    add basic arithmetic operations
arch/mips/isa/formats/fp.format:
    change Integer -> FP words
arch/mips/isa/formats/int.format:
    Add derived IntImm class
arch/mips/isa/operands.def:
    change to MIPS sytle operands

--HG--
rename : arch/mips/isa/formats/fpop.format => arch/mips/isa/formats/fp.format
rename : arch/mips/isa/formats/integerop.format => arch/mips/isa/formats/int.format
extra : convert_revision : a95da47bc981e56a9898421da4eeb9c442d1dc15