TF-M: Update docker image to include missing deps

TF-M currently failing on fatal error: bits/libc-header-start.h: No such
file or directory this should fix that.

Signed-off-by: Benjamin Copeland <ben.copeland@linaro.org>
Change-Id: Ia396b88761a1e1f3fa7c6656482ec52e1769b9a5
diff --git a/bionic-amd64-tf-m-build/Dockerfile b/bionic-amd64-tf-m-build/Dockerfile
index e81b020..3ac9b32 100644
--- a/bionic-amd64-tf-m-build/Dockerfile
+++ b/bionic-amd64-tf-m-build/Dockerfile
@@ -9,6 +9,8 @@
     default-jre \
     device-tree-compiler \
     doxygen \
+    g++-multilib \
+    gcc-multilib \
     git \
     graphviz \
     jq \