x86: kprobes change kprobe_handler flow

Make the control flow of kprobe_handler more obvious.

Collapse the separate if blocks/gotos with if/else blocks
this unifies the duplication of the check for a breakpoint
instruction race with another cpu.

Create two jump targets:
	preempt_out: re-enables preemption before returning ret
	out: only returns ret

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>