board/pca1000[0|5]: enabled RNG peripheral
cpu/nrf51822: added RNG driver
cpu/stm32f4: added random number generator driver
board/stm32f4discovery: enabled RNG driver
Merge pull request #1611 from haukepetersen/add_stm32f4_random

cpu/stm32f4: added random number generator driver
Merge pull request #1607 from haukepetersen/add_nrf_random

cpu/nrf51822: added random number generator driver