Benjamin Valentin f037e06b13 cpu/saml21: enable buck voltage regulator when possible
Switch from the on-chip LDO to the on-chip buck voltage regulator
when not fast internal oscillators are used.

On `saml21-xpro` with `examples/default` this gives

**before:** 750 µA
** after:** 385 µA
2020-04-02 17:25:16 +02:00
..
2020-04-02 17:25:13 +02:00
2020-03-31 13:39:41 +02:00