3.1 Errata Section in Data Sheet is no Longer Valid

A clarification for the Errata section in the device data sheet has been made.

The errata content has been moved to a separate document, ATxmega256A3U/192A3U/128A3U/64A3U Silicon Errata and Data Sheet Clarifications (this document).

See the Silicon Errata Issues section of this document for the latest errata.