linux-user/riscv: Add syscall riscv_hwprobe

linux-user/riscv: Add syscall riscv_hwprobe

This patch adds the new syscall for the
"RISC-V Hardware Probing Interface"
(https://docs.kernel.org/riscv/hwprobe.html).

Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Robbin Ehn <rehn@rivosinc.com>
Message-Id: <06a4543df2aa6101ca9a48f21a3198064b4f1f87.camel@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>