cpu: moved reboot_arch for cortex cpus
cpu/cortex-mX_common: fixed reboot_arch return val
cpu/cortex-mX_common: added delay to reboot_arch
Merge pull request #2047 from haukepetersen/fix_cortex_reboot

cpu: fixed and moved reboot_arch for cortex cpus
Basic DAC Driver, implementation on stm32f4discovery