binman: Use 'files-compress' to set compression for files

At present we use 'compress' as the property to set the compression of
a 'files' entry. But this conflicts with the same property for entries,
of which Entry_section is a subclass.

Strictly speaking, since Entry_files is in fact a subclass of
Entry_section, the files can be compressed individually but also the
section (that contains all the files) can itself be compressed. With this
change, it is possible to express that.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/085_files_compress.dts b/tools/binman/test/085_files_compress.dts
index 847b398..5aeead2 100644
--- a/tools/binman/test/085_files_compress.dts
+++ b/tools/binman/test/085_files_compress.dts
@@ -5,7 +5,7 @@
 	binman {
 		files {
 			pattern = "files/*.dat";
-			compress = "lz4";
+			files-compress = "lz4";
 		};
 	};
 };