Low Latency Mode Added

In SAM L21B there is a new configuration option in the HMATRIX to make a choice between low latency/high performance connection to a peripheral bus or a higher latency connection with a lower power consumption. Refer to Chapter "Features" in the SAM L21 datasheet for details on use of this feature. The default reset value gives the higher latency/lower power option, which is the same behavior as in SAM L21A.