avr32: pm: Fix section mismatch

The power management has a section mismatch which leads to the following
warning during compilation:

WARNING: arch/avr32/mach-at32ap/built-in.o(.text+0x16d4): Section
mismatch in reference from the function avr32_pm_offset() to the
function .init.text:pm_exception()
The function avr32_pm_offset() references
the function __init pm_exception().

Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Hans-Christian Egtvedt <hegtvedt@cisco.com>