Move and rename riscv_cpu_two_stage_lookup, to match
the other mmuidx_* functions.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Tested-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230325105429.1142530-15-richard.henderson@linaro.org>
Message-Id: <20230412114333.118895-15-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>