Changed MIPS and Alpha to pass the syscall number to the syscall function

Changed MIPS and Alpha to pass the syscall number to the syscall function

arch/alpha/isa/decoder.isa:
    Fixed up Alpha to pass the syscall number directly to the syscall function.
arch/mips/isa/decoder.isa:
    Fixed up MIPS to pass the syscall number directly to the syscall function.
arch/mips/isa/operands.isa:
    Added an R2 operand which is passed to the syscall function as the syscall number to use.

--HG--
extra : convert_revision : 066d486cd6a2761b29e413c6d526c268788975f3