xen: add framebuffer backend driver (Gerd Hoffmann)

xen: add framebuffer backend driver (Gerd Hoffmann)

This patch adds a frsamebuffer (and kbd+mouse) backend driver.  It
it based on current xen-unstable code.  It has been changed to make
use of the common backend driver code.  It also has been changed to
compile with xen headers older than release 3.3

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@7222 c046a42c-6fe2-441c-8c8c-71466251a162