Dockerfile: Update to a more current TF-A release tag

In preparation for using TF-A more in our CI loops, switch to the
current release tag for TF-A.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/tools/docker/Dockerfile b/tools/docker/Dockerfile
index 80bc2a9..e7be4e5 100644
--- a/tools/docker/Dockerfile
+++ b/tools/docker/Dockerfile
@@ -231,7 +231,7 @@
 # Build fiptool
 RUN git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git /tmp/tf-a && \
 	cd /tmp/tf-a/ && \
-	git checkout v2.10.0 && \
+	git checkout v2.12.0 && \
 	cd tools/fiptool && \
 	make -j$(nproc) && \
 	mkdir -p /usr/local/bin && \