Switch to using -1 on the UC3 target to obtain a register mask with all bits set (for clearing interrupts and status flags).
Fix incorrect USB controller mode on the UC3 when a fixed mode is specified as a compile time option due to AVR32_USBB.USBCON.uide being set by default.
Make USB_Descriptor_String_t use a uint16_t for Unicode strings on all targets except the AVR8 (retained for backwards compatibility).
Remove UC3B temp macros related to EEPROM, to ensure that projects requiring this break at compile time rather than at runtime until a solution can be found.