These functions are much closer to the softmmu helper
functions, in that they take the complete MemOpIdx,
and from that they may enforce required alignment.

The previous cpu_ldst.h functions did not have alignment info,
and so did not enforce it.  Retain this by adding MO_UNALN to
the MemOp that we create in calling the new functions.

Note that we are not yet enforcing alignment for user-only,
but we now have the information with which to do so.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>