ARM: 8071/1: perf: Make perf use arm_get_current_stackframe

Make the perf backend use the API so that it correctly references the FP
when in THUMB2 mode

Signed-off-by: Nikolay Borisov <Nikolay.Borisov@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>