cpu: Implement SPI driver for sam3x8e
boards: Implement SPI definitions for arduino-due
Merge pull request #1584 from PeterKietzmann/add_sam3x_spi

cpu/board: updated  spi driver for arduino-due
nativenet: Apply coding conventions
nativenet: Supply net_dev_t support for nativenet
netdev.tests: Remove unneccessary #ifndef path