Regression: partial revert "tracing: Remove lock_depth from event entry"

This partially reverts commit e6e1e2593592a8f6f6380496655d8c6f67431266.

That commit changed the structure layout of the trace structure, which
in turn broke PowerTOP (1.9x generation) quite badly.

I appreciate not wanting to expose the variable in question, and
PowerTOP was not using it, so I've replaced the variable with just a
padding field - that way if in the future a new field is needed it can
just use this padding field.

Signed-off-by: Arjan van de Ven <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/ftrace_event.h

···
 	unsigned char		flags;
 	unsigned char		preempt_count;
 	int			pid;
+	int			padding;
 };
 
 #define FTRACE_MAX_EVENT						\

kernel/trace/trace.c

···
 
 	entry->preempt_count		= pc & 0xff;
 	entry->pid			= (tsk) ? tsk->pid : 0;
+	entry->padding			= 0;
 	entry->flags =
 #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT
 		(irqs_disabled_flags(flags) ? TRACE_FLAG_IRQS_OFF : 0) |

kernel/trace/trace_events.c

···
 	__common_field(unsigned char, flags);
 	__common_field(unsigned char, preempt_count);
 	__common_field(int, pid);
+	__common_field(int, padding);
 
 	return ret;
 }