The internal DC/DC converter is more efficient compared to the LDO
regulator. The downside of the DC/DC converter is that it requires an
external inductor to be present on the board. Enabling the DC/DC
converter is guarded with NRF5X_ENABLE_DCDC, this macro must be defined
if the DC/DC converter is to be enabled.
- Removed stdio_init() from newlib's _init(), as this is too late in the boot
process to allow DEBUG()ing during periph_init()
- Added stdio_init() to the various cpu_init() routines of the ARM CPUs just
before periph_init()
