ARM: 8074/1: traps: Make use of the frame_pointer macro

Use the newly-introduced frame_pointer macro to extract
the correct FP based on whether we are in THUMB2 mode or not.

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>