The current ATxmega clock_init enable DFLL to improve the accuracy of
the 2MHz and 32MHz internal oscillators. In some ATxmega revisions,
after started DFLL the clock become unstable. Add another sync point
for 32MHz internal oscilator.
Note: If clock is not stable, system won't switch from 2MHz to 32MHz
as main clock.
Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>