Added COPYING and README.patch files to xen/common and xen/tools

Added COPYING and README.patch files to xen/common and xen/tools

This patch adds information related to non-GPL licenses and code
imports from 3rd party projects. The aim of this patch, is to
make it easier for future contributors, to perform a review
of the codebase.

Signed-off-by: Lars Kurth <lars.kurth@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
[ wei: remove all trailing whitespaces ]
Signed-off-by: Wei Liu <wei.liu2@citrix.com>