logging: basic API for logging with time stamps

To facilitate logging levels and assist with debugging we need a logging
API. This should suffice to cover the basic needs for both of those use
cases by prefixing each message with the time since the CPU started and
allowing the user to filter on log level.
logging: wire up existing debug msgs to API

Wire up some of the existing debug messages to the logging API so they
can be more finely controlled at runtime.