binman: Move compression into the Entry base class

Compression is currently available only with blobs. However we want to
report the compression algorithm and uncompressed size for all entries,
so that other entry types can support compression. This will help with
the forthcoming 'list' feature which lists entries in the image.

Move the compression properties into the base class. Also fix up the docs
which had the wrong property name.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/README b/tools/binman/README
index fe734c1..abbf809 100644
--- a/tools/binman/README
+++ b/tools/binman/README
@@ -339,6 +339,10 @@
 	limited by the size of the image/section and the position of the next
 	entry.
 
+compress:
+	Sets the compression algortihm to use (for blobs only). See the entry
+	documentation for details.
+
 The attributes supported for images and sections are described below. Several
 are similar to those for entries.
 
@@ -649,15 +653,16 @@
 -----------
 
 Binman support compression for 'blob' entries (those of type 'blob' and
-derivatives). To enable this for an entry, add a 'compression' property:
+derivatives). To enable this for an entry, add a 'compress' property:
 
     blob {
         filename = "datafile";
-        compression = "lz4";
+        compress = "lz4";
     };
 
 The entry will then contain the compressed data, using the 'lz4' compression
-algorithm. Currently this is the only one that is supported.
+algorithm. Currently this is the only one that is supported. The uncompressed
+size is written to the node in an 'uncomp-size' property, if -u is used.