Note that the specification for lf.madd.s is confused.  It's
the only mention of supposed FPMADDHI/FPMADDLO special registers.
On the other hand, or1ksim implements a somewhat normal non-fused
multiply and add.  Mirror that.
Reviewed-by: NBastian Koppelmann <kbastian@mail.uni-paderborn.de>
Signed-off-by: NRichard Henderson <rth@twiddle.net>