target/arm: Add ptw_idx to S1Translate

target/arm: Add ptw_idx to S1Translate

Hoist the computation of the mmu_idx for the ptw up to
get_phys_addr_with_struct and get_phys_addr_twostage.
This removes the duplicate check for stage2 disabled
from the middle of the walk, performing it only once.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20221024051851.3074715-3-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>