avr32: select generic atomic64_t support

commit 31e0017e6f6fb5cfdfaf932c1f98c9bef8d57688 upstream.

Enable use of the generic atomic64 implementation on AVR32 platforms.
Without this the kernel fails to build as the architecture does not
provide its version.

Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>