link/graphics: add functions to support aux channel communications

For full integration of FUI into coreboot, we need aux channel
communcations.  The intel_dp.c is a file taken from Linux and is
used for aux channel comms.  This file has been cut down to work
with coreboot.  For now it is associated with the link mainboard
until we get a better handle on how this all fits together.  This
code is almost certainly usable on other platforms in the long term.
But one step at a time.

Change-Id: I7be4c56e0a7903f3901ac86e12b28f3bdc0f7947
Signed-off-by: Ronald G. Minnich <rminnich@google.com>
Reviewed-on: http://review.coreboot.org/2834
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/google/link/i915io.c

@@ -16,7 +16,7 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  */
-
+#include <stdint.h>
 #include "i915io.h"
 
 struct iodef iodefs[] = {