bootstrap/clocks: support CS4 and refine LED-based diagnostics
bootstrap/clocks: support CS4 and refine LED-based diagnostics

Provide feedback that we made it past basic initialization, and expose
the clocks immediately afterward so we can diagnose clock issues before
we have a working console.  Also put in support for the FR4xx variant of
the CS peripheral.

pabigot/bsp430,pabigot/bsp430,pabigot/bsp430,pabigot/bsp430