i386: make callgraph use dump_trace() on i386/x86_64

This patch improves oprofile callgraphs for i386/x86_64. The old
backtracing code was unable to produce kernel backtraces if the
kernel wasn't compiled with framepointers. The code now uses
dump_trace().

[ 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>