avr32: remove cpu_data macro to fix compiles

Having cpu_data as a parameterless macro can easily cause build failures
because it can be a variable name like in linux/pm_domain.h [1]. So,
remove the macro and convert its only user. Because this architecture
cannot do SMP, remove the whole SMP block, too. Only compile tested due
to no hardware.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>

[1] https://lists.01.org/pipermail/kbuild-all/2014-February/003252.html