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.
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>
