STM32 DMAv1 driver.

Driver capability:

- The driver supports the STM32 traditional DMA controller in the following
  configurations: 5ch, 7ch, 7ch+5ch.
- 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 if CSELR is present.
STM32_DMAn_NUM_CHANNELS     - Number of channels in DMA1.
STM32_DMAn_CHx_HANDLER      - Vector name for IRQ "x".
STM32_DMAn_CHxyz_HANDLER    - Vector name for shared IRQs "x", "y" and "z".
STM32_DMAn_CHx_NUMBER       - Vector number for IRQ "x".
STM32_DMAn_CHxyz_NUMBER     - Vector number for shared IRQs "x", "y" and "z".

Currently supported shared combinations are:

STM32_DMA1_CH23_HANDLER
STM32_DMA1_CH23_NUMBER
STM32_DMA1_CH4567_HANDLER
STM32_DMA1_CH4567_NUMBER