of: update ePAPR references to point to Devicetree Specification

The Devicetree Specification has superseded the ePAPR as the
base specification for bindings.  Update files in Documentation
to reference the new document.

First reference to ePAPR in Documentation/devicetree/bindings/arm/cci.txt
is generic, remove it.

Some files are not updated because there is no hypervisor chapter
in the Devicetree Specification:
   Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt
   Documenation/virtual/kvm/api.txt
   Documenation/virtual/kvm/ppc-pv.txt

Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>