Flattened device headers to relevant family module
Device/SiliconLabs/EFM32XX headers and source files relocated to cpu/efm32xx. Removed non-gcc linker and startup scripts.
Moved riot cortex family includes to efm families
efm32xx family includes now include the correct cortex-mX_common module
Updated for EFM32ZG support
Build tools work correctly, hardfault during initialisation (presumed due to unaligned memory access), needs to be debugged.