[PATCH] x86_64: reliable stack trace support (x86-64 IRQ stack

Change the switching to/from the IRQ stack so that unwind annotations can
be added for it without requiring CFA expressions.

AK: I cleaned it up a bit, making it unconditional and removing the
obsolete DEBUG_INFO full frame code.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>