feat: add STM32U073C(8-B-C) and STM32U083CC generic board support

[ndoo]

Summary

This PR adds support for the STM32U073C(8-B-C) and STM32U083CC parts of the STM32U0 series.

This PR fixes/implements the following bugs/features

• Feature: STM32U073C(8-B-C) and STM32U083CC generic board support

STM32U073C(8-B-C) and STM32U083CC generic board support was not added to boards.txt in #2495, but the variant files supporting it are mostly in place. This adds the boards.txt definition, linker script and clock configuration, which completes the support within Arduino.

Validation

CheckVariant.ino serial output on STM32U073CC:

#####
NUM_DIGITAL_PINS = 39
NUM_ANALOG_INPUTS = 10
#####
Checking digital pins...
End check digital pins
#####
Checking analog pins definition...
End check analog pins
#####
Checking IP instances (I2C, UART, SPI)...
End check IP instances (I2C, UART, SPI)

########################################
#### Test PASSED
########################################

[fpistm]

Hi @ndoo
Thanks for the PR.
Please see my comments.

[ndoo]

Hi @ndoo Thanks for the PR. Please see my comments.

Welcome @fpistm, force-pushed with incorporated review feedback, please review.