target/s390x: Implement s390x_cpu_record_sigbus

For s390x, the only unaligned accesses that are signaled are atomic,
and we don't actually want to raise SIGBUS for those, but instead
raise a SPECIFICATION error, which the kernel will report as SIGILL.

Split out a do_unaligned_access function to share between the user-only
s390x_cpu_record_sigbus and the sysemu s390x_do_unaligned_access.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/s390x/cpu.c

@@ -269,6 +269,7 @@ static const struct TCGCPUOps s390_tcg_ops = {
 
 #ifdef CONFIG_USER_ONLY
     .record_sigsegv = s390_cpu_record_sigsegv,
+    .record_sigbus = s390_cpu_record_sigbus,
 #else
     .tlb_fill = s390_cpu_tlb_fill,
     .cpu_exec_interrupt = s390_cpu_exec_interrupt,