Add support for STM32C071Rx

[fpistm]

STM32C071R8
STM32C071RB

Or if it needs to be more specific, those pages under Sample & Buy contains these:
STM32C071RBT6N
STM32C071RBI6N
STM32C071RBT6
STM32C071R8T6
STM32C071R8T6N
STM32C071R8I6N

STM32C071RBT6 is the one I am personally most interested in.

Originally posted by @thernstig in #722 (comment)

[fpistm]

Added to the list #722