target/riscv: Use tcg_constant_*

target/riscv: Use tcg_constant_*

Replace uses of tcg_const_* with the allocate and free close together.

Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210823195529.560295-2-richard.henderson@linaro.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>