Add flashmap to manifest

Needed to compile the sdk

BUG=b/177367546
TEST=repo init, repo sync, `sudo emerge flashmap`
RELEASE_NOTE=None

Change-Id: Iee5c9da3c0996fc0788d12b62bfe298b5a8cca00
Reviewed-on: https://cos-review.googlesource.com/c/cos/manifest/+/29980
Tested-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Dexter Rivera <riverade@google.com>
(cherry picked from commit 9fb090b5ade231af3c84b934123d3683d1423405)
Reviewed-on: https://cos-review.googlesource.com/c/cos/manifest/+/33520
Reviewed-by: He Gao <hegao@google.com>

external_full.xml

diff --git a/external_full.xml b/external_full.xml
index f07c70b..35bfe8a 100644
--- a/external_full.xml
+++ b/external_full.xml
@@ -66,6 +66,9 @@
   <project path="src/third_party/u-boot/files"
            name="mirrors/cros/chromiumos/third_party/u-boot"
            revision="39ce6d27ad29fd324793a8d0c7db8ae712cc027c" />
+  <project path="src/third_party/flashmap"
+           name="mirrors/cros/chromiumos/third_party/flashmap"
+           revision="9c71c8331ad52a11d29496ffb10cbdb1a51e2ccb" />
 
   <!-- COS sources -->
   <project path="src/overlays"