This commit adds initial support for STM32H5xx MCUs. The following
features have been confirmed to be working on an STM32H573:
- UART over REPL and USB CDC
- USB CDC and MSC
- internal flash filesystem
- machine.Pin
- machine.SPI transfers with DMA
- machine.ADC
- machine.RTC
- pyb.LED
- pyb.Switch
- pyb.rng
- mboot
Signed-off-by: Damien George <damien@micropython.org>
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