Add instructions of RR1 opcode format, that have 0xb3 as first opcode.
Add helper functions mulh, mulmh and mulrh, that compute multiplication,
with multiprecision (mulmh) or rounding (mulrh) of 4 halfwords, being either low or high parts
of two 32 bit regs.
Signed-off-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Reviewed-by: Richard Henderson <rth@twiddle.net>
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