Reset Value of CTRLB.MANW Changed

In SAM L21B the reset value of the Manual Write bit in the Control B register of the NVM peripheral (NVM.CTRLB.MANW) has been changed from 0 to 1. This was done to avoid corrupting system flash. With automatic write, when writing to a bad pointer pointing to flash it was possible to corrupt the flash data. By default this is not possible in SAM L21B.