arch/arm/include/stm32f0l0g0: add support for STM32G070CB, STM32G070KB, STM32G070RB
arch/arm/src/stm32f0l0g0: add support for STM32G070CB, STM32G070KB, STM32G070RB
Squashed commit of the following:
arch/arm: Rename include/stm32f0l0 and src/stm32f0l0 to stm32f0l0g0.
Change all occurrences of lower-case stm32f0l0 to stm32f0l0g0.
Change all occurrences of upper-case STM32F0L0 to STM32F0L0G0.