target/riscv: support for 128-bit shift instructions

target/riscv: support for 128-bit shift instructions

Handling shifts for 32, 64 and 128 operation length for RV128, following the
general framework for handling various olens proposed by Richard.

Signed-off-by: Frédéric Pétrot <frederic.petrot@univ-grenoble-alpes.fr>
Co-authored-by: Fabien Portas <fabien.portas@grenoble-inp.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20220106210108.138226-13-frederic.petrot@univ-grenoble-alpes.fr
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>