There is no hardware limitation for custom boards based on STM32 to uses
SPI bus with signals coming from different PORT and alternate functions.
This patch allow alternate's function definition per pin basis, thus enable
the support of SPI bus signals routed on differents PORT.
Signed-off-by: Yannick Gicquel <ygicquel@gmail.com>
- 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