Whenever any of the defmt-timestamp-uptime* features is enabled, defmt
will insert code that reads the timestamp in order to embed it into
the format string. This means that we *must* have a functional time
driver by the time the very first defmt message is printed.
Because clocks.rs is the part of the code setting up clocks that may,
indeed, be required by the chosen clock driver, it cannot contain any
defmt messages, otherwise it will trigger a read to a function that
does not yet exist.
Signed-off-by: Felipe Balbi <febalbi@microsoft.com>