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>