samr21: 32 hwtimer

The hwtimer did not work correctly on the samr21-xpro, I accidentally read that it has to use a 32 bit timer,
So I changed the timer peripheral to have 1 16-bit timer and 1 32-bit timer, and the hwtimer is now using the 32 bit timer.

For the HWTIMER this value should be `125000` as the hwtimer takes care of the `-1` as far as I know... But this value seems also awfully slow to me, most of our timers run at 1MHz...