Add the STM32G0 to the CMake setup. This CMake is specific to the STM32G0B1xK device. Also included the linker file that is required for the make.
Currently G0 targets are disabled by default to keep project buildable
as-is.
This had probably been accidentally reverted in
2ebc665109887bfe95a4ad63ebe5e1d7d13c0fef ? flash_data_rom ended up on the same flash page as other unrelated data, which meant flash_flush() would've erased too much.
Also reduce nvm area to 1k and use variables to calculate area. (F042
devices only have 1kB pages vs 2k for the F072)
