The current xmega don't have a way to disable peripherals that are
not in used. Add peripheral management to allow enable only the mcu
blocks that will be used by application. This saves power on active
and sleep modes. By default, at clock initialization, all peripherals
are now disabled and each drive must activate at initialization phase.
The periph_timer and periph_uart were updated with this new feature.
Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>
