Add mesa-amd repo

BUG=b:146054156
TEST=repo sync, third_party/mesa-amd is there

Change-Id: I7c5bb4ae50109f98453583021b02f285b516c3ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/manifest/+/1962487Tested-by: Drew Davenport <ddavenport@chromium.org>
Reviewed-by: Dhanya Ganesh <dhanyaganesh@chromium.org>
Commit-Queue: Drew Davenport <ddavenport@chromium.org>

full.xml

@@ -392,6 +392,9 @@ Your sources have been sync'd successfully.
            name="chromiumos/third_party/marvell" />
   <project path="src/third_party/mesa"
            name="chromiumos/third_party/mesa" />
+  <project path="src/third_party/mesa-amd"
+           name="chromiumos/third_party/mesa"
+           revision="refs/heads/chromeos-amd" />
   <project path="src/third_party/mesa-debian"
            name="chromiumos/third_party/mesa"
            revision="refs/heads/debian" />