native: add periph substructure
native: relocate periph/cpuid implementation
native: add drivers substructure
native: relocate drivers/rtc implementation
cc2538: Set __NVIC_PRIO_BITS to the correct value of 3.
Merge pull request #1838 from LudwigOrtmann/native_subsstructure

native: add substructure
Merge pull request #1848 from locicontrols/cc2538-nvic-prio-bits

cc2538: Set __NVIC_PRIO_BITS to the correct value of 3.
byteorder: silence warnings in clang
Merge pull request #1852 from authmillenon/byteorder-silence

byteorder: silence warnings in clang
Merge branch 'master' of https://github.com/RIOT-OS/RIOT into efm32-support