AT91lib update

Updates selected portions of AT91lib to version 1.8, in order to fix SD data corruption.
Changes the board's master clock from 48mhz to 96mhz.

This was done as a partial update, rather than simply by updating all of AT91lib, because version 1.8 introduces changes to USB communications that are not compatible with 4pi (or which were intended for another processor, and simply don't work with SAM3U).