[STM32] use DMA in USB host driver

[pierstitus]

For performance it would be good to use DMA in the USB host driver.

Currently the STM USB host library doesn't support hubs, and the ChibiOS-Contrib USB host driver doesn't use DMA, so it would be very valuable to have DMA in here, so one doesn't have to choose between performance and hub support.

[dismirlian]

Hi @pierstitus, just to note that the current USB Host stack doesn't use DMA because the full speed OTG module in the STM32 doesn't have DMA support. So, one driver fits all...

Adding DMA would be great!

Diego.