STM32F4: FMPI2C doesn't work about mbed-os HOT 6 OPEN

@mikrodust-henrikp thank you for raising this issue.Please take a look at the following comments:

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Maybe it's known, since I found mentions regarding this in the forums: https://forums.mbed.com/t/not-working-fmpi2c1-stm32f446re-nucleo-f446re-fmpi2c/7890

But it seems wrong that it fails silently, and of course would be even better if it actually worked.

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@jeromecoutant would you know about FMPI2C1 ?

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@jeromecoutant would you know about FMPI2C1 ?

No... maybe this is why it has not been supported yet with mbed-os :-)

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I suppose I should remove all FMPI2C_1 pins from https://github.com/ARMmbed/mbed-os/blob/master/targets/TARGET_STM/TARGET_STM32F4/TARGET_STM32F412xG/TARGET_NUCLEO_F412ZG/PeripheralPins.c#L84-L116

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We have a custom target and the STM32_gen_PeripheralPins.py will happily generate FMPI2C definitions in PeripheralPins. So..maybe solved for some targets that way, but not all. Also the https://github.com/ARMmbed/mbed-os/blob/master/targets/TARGET_STM/i2c_api.c has some clock setup and things related to FMPI2C which sort of indicates that it should work, but maybe it should be made to fail with MBED_ERROR or something if FMPI2C1 is encountered, or something.

Even better would be to fix i2c_read/i2c_write to use the fmpi2c HAL API that seems to be working just fine, but I don't know how well that'll work with the i2c_byte_read et al..if at all.

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