binman: Add support for Chromium GBB

This entry contains a Google Binary Block, used to store keys and bitmaps
in a Chromium image.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/72_gbb_too_small.dts b/tools/binman/test/72_gbb_too_small.dts
new file mode 100644
index 0000000..c088f36
--- /dev/null
+++ b/tools/binman/test/72_gbb_too_small.dts
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0+
+/dts-v1/;
+
+/ {
+	binman {
+		gbb {
+			size = <0x200>;
+		};
+	};
+};