s390x/tcg: Handle all rounding modes overwritten by BFP instructions

s390x/tcg: Handle all rounding modes overwritten by BFP instructions

"round to nearest with ties away from 0" maps to float_round_ties_away.
"round to prepare for shorter precision" maps to float_round_to_odd.

As all instructions properly check for valid rounding modes in translate.c
we can add an assert. Fix one missing empty line.

Cc: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190218122710.23639-15-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>