Unaligned traps are optional, but required with an mmu.
Turn them on always, because the fallback behaviour undefined.

Enable alignment checks in the config file.
Unwind the guest pc properly from do_unaligned_access.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220421151735.31996-48-richard.henderson@linaro.org>