binman: capsule: Add support for generating EFI empty capsules

Add support in binman for generating EFI empty capsules. These
capsules are used in the FWU A/B update feature. Also add test cases
in binman for the corresponding code coverage.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/320_capsule_revert.dts b/tools/binman/test/320_capsule_revert.dts
new file mode 100644
index 0000000..bd141ef
--- /dev/null
+++ b/tools/binman/test/320_capsule_revert.dts
@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/dts-v1/;
+
+/ {
+	binman {
+		efi-empty-capsule {
+			capsule-type = "revert";
+		};
+	};
+};