binman: Support compressed entries

Add support for compressing blob entries. This can help reduce image sizes
for many types of data. It requires that the firmware be able to
decompress the data at run-time.

Signed-off-by: Simon Glass <sjg@chromium.org>

.travis.yml

@@ -27,6 +27,7 @@ addons:
     - wget
     - device-tree-compiler
     - lzop
+    - liblz4-tool
 
 before_install:
  - sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y