drivers: Initial import of SPI low-level driver IF
drivers: fixes to the SPI low-level interface
driver: updated SPI driver interface
Merge branch 'add_driver_spi_if' of https://github.com/haukepetersen/RIOT into stm32f4_spi_driver
edited spi define
added dirs in stm32f4 makefile
added drivers folder in stm32f4
removed spi driver from boards folder. prep. to put it into cpu
added spi driver to cpu folder
added test for spi interface and prep. nrf24l01+
changed the st-registers include file to stm32f407xx.h
blacklist all boards except stm32f4discovery in project makefile
blacklist native in project makefile
remove space line
spaces instead of tabs
deleted unused defines
edited copyrigth header
[SQUASH ME] added fixed speed values
reduced register setting code; enabling in initialisation function
changed SPI_port to spi_port