Support STM32U0 Family

[xanthio]

Bring STM32U0 family support to project

[atsju]

I did not check the Flash sizes as I usually do but this looks high quality PR. Thank you.
@Hish15 I let you merge if it's OK for you

[xanthio]

I did not check the Flash sizes as I usually do but this looks high quality PR. Thank you. @Hish15 I let you merge if it's OK for you

Actually, Flash size variants for this family is weird as we can find 16/32/64M of Flash but it depends the package:
U031C6
U031C8
U031F4
U031F6
U031F8
U031G6
U031G8
U031K4
U031K8
U031R6
U031R8

Do you think there is an interest in splitting this subfamilly ?

[atsju]

I checked your code is actually correct.
example: U031C6 => U031 gives RAM size because is a specific subfamily and here all the subfamily has same RAM (cool, not always the case)
C => package => no interrest for us in this case. Sometimes it has an effect
6 => flash size. See file common.cmake

[xanthio]

@Hish15 Is there an issue for not merging this PR ?

I'm starting a project with STM32U0 target and would really like to submodule this before.

[Hish15]

Seems good to me, solve the conflict and we are good to go!

[xanthio]

I didn't notice #337 breaked this
This should be OK now.