FWU: cmd: Add a command to read FWU metadata

Add a command to read the metadata as specified in the FWU
specification and print the fields of the metadata.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index c601d35..df50746 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -50,6 +50,7 @@
    cmd/fdt
    cmd/font
    cmd/for
+   cmd/fwu_mdata
    cmd/gpio
    cmd/load
    cmd/loadm