binman: Support alignment of files

When packing files it is sometimes useful to align the start of each file,
e.g. if the flash driver can only access 32-bit-aligned data. Provides a
new property to support this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/084_files.dts b/tools/binman/test/084_files.dts
index 83ddb78..8f09afd 100644
--- a/tools/binman/test/084_files.dts
+++ b/tools/binman/test/084_files.dts
@@ -5,7 +5,7 @@
 	binman {
 		files {
 			pattern = "files/*.dat";
-			compress = "none";
+			files-compress = "none";
 		};
 	};
 };