STM32 DMAv1 driver.

Driver capability:

- The driver supports the STM32 traditional DMA controller in the following
  configurations: 5ch, 7ch, 7ch+5ch, 7ch+7ch.
- Support for automatic the channel selection through the CSELR register.
- For devices without CSELR register it is possible to select channels but
  the SYSCFG CFGR register is not configured, the user has to configure it
  before starting the DMA driver.
- The driver supports shared ISR handlers with a quirk: the IRQ priority is
  established by the first allocated channel among the channels sharing the
  ISR.

The file registry must export:

STM32_ADVANCED_DMA          - TRUE not used by the DMA drivers but other
                              drivers use it to enable checks on DMA
                              channels. Probably will be removed in the
                              future.
STM32_DMA_SUPPORTS_CSELR    - TRUE if the DMA have a CSELR register.
STM32_DMAn_NUM_CHANNELS     - Number of channels in DMAs "n" (1..2).
STM32_DMAn_CHx_HANDLER      - Vector name for IRQ "x" (1..7). If the macro
                              is not exported then the ISR is not declared.
STM32_DMAn_CHx_NUMBER       - Vector number for IRQ "x" (1..7).
