RISC-V: Move non-ops from op_helper to cpu_helper

RISC-V: Move non-ops from op_helper to cpu_helper

This patch makes op_helper.c contain only instruction
operation helpers used by translate.c and moves any
unrelated cpu helpers into cpu_helper.c. No logic is
changed by this patch.

Signed-off-by: Michael Clark <mjc@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>