conf/machine/parallella: Refactored exists machine conf

* Remove the "gen0" machine conf, the parallella machine is capable of
  dealing with the multiple generations via device trees.
* Add device tree for the production release of the Parallella.
* Split out the device trees into dtsi files.
* Update README.
linux-adi: Add the linux-adi kernel from the Parallella repo

* This is setup on the "bcxcube_epiphany_driver" branch to have support
  for the Epiphany driver which is required for the newer epiphany-libs.
* Force the CONFIG_EPIPHANY=y