target/riscv: Set MMU_2STAGE_BIT in riscv_cpu_mmu_index

target/riscv: Set MMU_2STAGE_BIT in riscv_cpu_mmu_index

Incorporate the virt_enabled and MPV checks into the cpu_mmu_index
function, so we don't have to keep doing it within tlb_fill and
subroutines.  This also elides a flush on changes to MPV.

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: <20230325105429.1142530-17-richard.henderson@linaro.org>
Message-Id: <20230412114333.118895-17-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>