The MSP430 vendor files already provide macros containing register
constants and symbols (provided via linker scripts) containing addresses
of peripheral registers. So lets make use of that rather than
maintaining a long list of constants.
Provide a common clock initialization driver rather than leaving
clock initialization to the boards code. A declarative description of
the board's clock configuration using a struct does still allow to
fine-tune settings. In addition, a board is still allowed to just
provide a custom `void clock_init(void)` if there really is the need
to do crazy things.
