Fix build warnings and use the Kbuild infrastructure for generic headers
rather than doing it by hand.
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/egtvedt/linux-avr32:
avr32: cast syscall_return to silence compiler warning
avr32: fix clockevents kernel warning
avr32: use Kbuild infrastructure to handle the asm-generic headers