target/arm: Implement arm_cpu_record_sigbus

target/arm: Implement arm_cpu_record_sigbus

Because of the complexity of setting ESR, re-use the existing
arm_cpu_do_unaligned_access function.  This means we have to
handle the exception ourselves in cpu_loop, transforming it
to the appropriate signal.

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