This introduces the extended opcode field for DS form instructions and the fields d0, d1 and d2 which are concatenated for specifying a signed integer immediate operand. Change-Id: Id60e85d79f9157d680f813bf90ab6e1e064253a9 Signed-off-by: Sandipan Das <sandipan@linux.ibm.com> Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40901 Reviewed-by: Boris Shingarov <shingarov@labware.com> Maintainer: Jason Lowe-Power <power.jg@gmail.com> Tested-by: kokoro <noreply+kokoro@google.com>