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>
diff --git a/src/mainboard/google/link/i915io.h b/src/mainboard/google/link/i915io.h
index 768bc7e..638d59e 100644
--- a/src/mainboard/google/link/i915io.h
+++ b/src/mainboard/google/link/i915io.h
@@ -58,3 +58,14 @@
 	unsigned long data;
 	unsigned long udelay;
 };
+
+/* i915.c */
+unsigned long io_i915_READ32(unsigned long addr);
+void io_i915_WRITE32(unsigned long val, unsigned long addr);
+
+/* intel_dp.c */
+u32 pack_aux(u8 *src, int src_bytes);
+void unpack_aux(u32 src, u8 *dst, int dst_bytes);
+int intel_dp_aux_ch(u32 ch_ctl, u32 ch_data, u8 *send, int send_bytes,
+	u8 *recv, int recv_size);
+