x86: introduce frame_pointer() and stack_pointer()

This patch defines frame_pointer() and stack_pointer() similar to the
already defined instruction_pointer(). Thus the oprofile code can be
written in a more readable fashion.

[ tglx: arch/x86 adaptation ]

Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>