target/riscv: Implement address masking functions required for RISC-V Pointer Masking...

target/riscv: Implement address masking functions required for RISC-V Pointer Masking extension

Signed-off-by: Anatoly Parshintsev <kupokupokupopo@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20211025173609.2724490-8-space.monkey.delivers@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>