arm64: Fix for ptrace instruction rewrite on thunder-x2.

- Fixed the problem that instruction rewriting by PTRACE_POKETEXT is not reflected.
   The cause is that the instruction cache was not flushed.

 - Add instruction chache flush in ptrace_report_signal().

Change-Id: Ie9d34d3d33e1fd85aef5fe419345d82c6ca781fb

arch/arm64/kernel/ptrace.c

@@ -1011,6 +1011,7 @@ void ptrace_report_signal(struct thread *thread, int sig)
 	if (sig == ((SIGTRAP | (PTRACE_EVENT_EXEC << 8)))) {
 		memcpy(thread->ctx.thread, &tinfo, sizeof(struct thread_info));
 	}
+	arch_flush_icache_all();
 }
 
 long