implement the Tcc instruction to call syscall.

implement the Tcc instruction to call syscall.

arch/sparc/isa/bitfields.isa:
    the trap field is 7:0
arch/sparc/isa/decoder.isa:
    add code to in the Tcc instruction to call a syscall
arch/sparc/isa_traits.hh:
    We need the syscall num register

--HG--
extra : convert_revision : 0861ec1dd8c7cac57765b22bc408fdffbe63fe2a