This PR sets the DMA configuration for the UART peripherals on the
stm32f4 boards to the undef value to disable the DMA. This to prevent
from accidentally configuring the DMA to stream 0 channel 0 when
enabling DMA.
- removed neccessity to define empty `DAC_NUMOF 0` for each STM
base board
- adapted all board configs to this
- joined stm32f2 to use common DAC driver
- improved code of DAC driver
* also added a trailing underscore to header guards for consistency
Commit for PR 2623, repairing header file include guards.
This PR is intended to fix the include guards in files under RIOT/boards
SQUASH ME: fix underscore removal overdos
SQUASH ME: consistent macro naming
SQUASH ME: missed that one
SQUASH ME: fixed overdo
SQUASH ME: consistency
