target/ppc: Move add and subf type fixed-point arithmetic instructions to decodetree

target/ppc: Move add and subf type fixed-point arithmetic instructions to decodetree

This patch moves the below instructions to decodetree specification:

        {add, subf}[c,e,me,ze][o][.]       : XO-form
        addic[.], subfic                   : D-form
        addex                              : Z23-form

This patch introduces XO form instructions into decode tree
specification, for which all the four variations([o][.]) have been
handled with a single pattern. The changes were verified by validating
that the tcg ops generated by those instructions remain the same, which
were captured with the '-d in_asm,op' flag.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Chinmay Rath <rathc@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>