Add NEUTRONRCF435 support including AT32F435RGT7 1M FLASH

[SteveCEvans]

The NEUTRONRCF435 uses the AT32F435RGT7 with 1Mbytes of FLASH rather than the AT32F435ZMT7 which has 4Mbytes. This PR adds support for both. The flash sector size is also 2K rather than 4K for the 1Mbyte part which was resulting in a boot loop.

A NEUTRONRCF435 config file is added but this will need amending with timer/dma/motor definitions.

BARO, OSD and FLASH are currently supported.

There are now two AT32F435 targets to accommodate 1Mbyte and 4Mbyte FLASH. config.h can specify the following for 4M devices

#define FC_TARGET_MCU     AT32F435M

or for 1M devices

#define FC_TARGET_MCU     AT32F435G

[blckmn]

AUTOMERGE: (FAIL)

• github identifies PR as mergeable -> FAIL
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[github-actions]

Do you want to test this code? Here you have an automated build:
Assets
WARNING: It may be unstable. Use only for testing! See: https://www.youtube.com/watch?v=I1uN9CN30gw for instructions for unified targets!