Move common logic into a default routine in platform/power that other
platforms can reuse to implement the general default shutdown logic.
Add helper routines to print the cause.
Refactor the platforms that had substantial halt logic to reuse the
default implementation.
Almost nothing changes here except moving braces to the same line as the
function declaration. Everything else is largely whitespace changes and
a few dangling files with tab indents.
See scripts/codestyle
