Add XMEGA support to the class driver demos where possible.
Add stub functions to all board drivers, so that demos can be compiled with BOARD=NONE.
Assume 16MHz crystal by default in the AVR8 bootloaders.
Add platform includes to the bootloaders.
Pseudo-port the projects and dual role demos for possible later multi-arch support.
Pseudo-port the host mode demos for possible later multi-arch support.
Port the device mode demos to the XMEGA architecture where applicable.
Add missing project dependencies.
Merge branch 'master' into XMEGA-Demo-Ports-ClockOnly
Merge branch 'XMEGA-Demo-Ports-ClockOnly'