The STM32 line of microcontrollers comes with a bootloader in the ROM.
It provides the option to flash the device firmware in DFU mode (USB)
or via UART or SPI.
To enter the bootloader we have to jump to a specific address in memory,
but before reset the CPU to make sure the system is in a known state.
This enables us to use the usb_board_reset module on all STM32 platforms.
This commit adds two new functions to the DMA peripheral code for the
stm32. The setup function allows for a one-time setup of peripheral
config. The prepare function does the per-transfer setup. This allows
for a single setup call during the peripheral lock step and a
per-transfer call to the prepare function.
`usbdev_stm32.h` will pull in `usb.h` which causes an error if
`USB_H_USER_IS_RIOT_INTERNAL` is not set.
Turns out this include is not needed, so just drop it.
