ext: hal: nordic: Add missing nordic header file needed by nrf_power.h

While importing the nrf_power.h to use the nrf_power_resetreas_get()
function the missing header file error was presented.

Origin: Nordic SDK 12.2.0 (components/drivers_nrf/hal)
URL: http://developer.nordicsemi.com/nRF5_SDK/


License: 3-clause BSD
Maintained-by: External

Signed-off-by: Flavio Arieta Netto <flavio@exati.com.br>
Signed-off-by: flavio <flavio@exati.com.br>