Fix missing ADC4 dma mapping for F3.

Fix missing ADC4 dma mapping for F3.

Fix incorrect count of dma options for F3.

Value was hardcoded to 3, but the F3 has 4 ADCs.

Fix dmaPeripheralMapping for F3.

The dmaPeripheralMapping table was using index numbers and not device
numbers.

This meant all the dma mappings were out by one, eg.

```

```

ADC 1 is on DMA1, channel 1, but the output from dma ADC 2 list shows
the possibilities for ADC 1, not ADC 2 and shows no possibilities for
dma ADC 1 list

Ensure there are defaults for ADC4 on F3.

Always use 4 ADC instances for the ADC PG.

* PG should not be target dependant.
* Add a static assert which will fail if anything is changed.

Fix dmaopt in ADC PG, it should be a int8_t, not uint8_t

Fix occurrences of -1 that should be `DMA_OPT_UNUSED`.

Fixing this meant that dma_reqmap.h needed to be included in a few
places.  When this was done there were errors because dma_reqmap.h was
included more than once and it's `#pragma once` was commented out.

Including dma_reqmap.h from every PG that uses `dmaopt` also caused
other compilation issues, fixed by this commit.