target/arm: Pass unpriv bool to get_a64_user_mem_index()

target/arm: Pass unpriv bool to get_a64_user_mem_index()

In every place that we call the get_a64_user_mem_index() function
we do it like this:
 memidx = a->unpriv ? get_a64_user_mem_index(s) : get_mem_index(s);
Refactor so the caller passes in the bool that says whether they
want the 'unpriv' or 'normal' mem_index rather than having to
do the ?: themselves.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20230912140434.1333369-4-peter.maydell@linaro.org