target/riscv: support for 128-bit U-type instructions

target/riscv: support for 128-bit U-type instructions

Adding the 128-bit version of lui and auipc, and introducing to that end
a "set register with immediat" function to handle extension on 128 bits.

Signed-off-by: Frédéric Pétrot <frederic.petrot@univ-grenoble-alpes.fr>
Co-authored-by: Fabien Portas <fabien.portas@grenoble-inp.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20220106210108.138226-12-frederic.petrot@univ-grenoble-alpes.fr
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>