Add helpers helper_subadr_h/_ssov which subs one halfword and adds one
halfword, rounds / and saturates each half word independently.

Add microcode helper functions:
    * gen_msubad_h/ads_h: multiply two halfwords left justified and sub from the
                          first one word and add the second one word
                          / and saturate each resulting word independetly.
    * gen_msubadm_h/adms_h: multiply two halfwords in q-format left justified
                            and sub from the first one word and add to
                            the second one word / and saturate each resulting
                            word independetly.
    * gen_msubadr32_h/32s_h: multiply two halfwords in q-format left justified
                             and sub from the first one word and add to
                             the second one word, round both results / and
                             saturate each resulting word independetly.
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NBastian Koppelmann <kbastian@mail.uni-paderborn.de>