tcg-arm: Avoid ldrd/strd for user-only emulation

The arm ldrd/strd insns must cause alignment traps, whereas
at least for armv7 ldr/str must handle unaligned operations.

While this is hardly the only problem facing user-only emu,
this solves one problem for i386 on armv7 emulation.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reported-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
Merge remote-tracking branch 'remotes/rth/tcg-arm-unaligned' into staging

* remotes/rth/tcg-arm-unaligned:
  tcg-arm: Avoid ldrd/strd for user-only emulation

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>