hw/timer/pl031: Convert to using trace events

hw/timer/pl031: Convert to using trace events

Convert the debug printing in the PL031 device to use trace events,
and augment it to cover the interesting parts of device operation.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>