Adds a driver for the Nordic nRF GPREGRET registers and adds
entries to the SoCs for this peripheral.
Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
Adds a new driver interface for retained memory devices which
can be used to store data and have it retained whilst the device is
powered thorugh different application execution states (though this
data may be lost in low power states).
Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>