west: bindesc: Added get_offset command

Add `west bindesc get_offset` command to print the offset of
the descriptors inside the given image.

Signed-off-by: Yonatan Schachter <[email protected]>

Author: yonsch

doc/develop/west/zephyr-cmds.rst

@@ -215,3 +215,7 @@ You can dump all of the descriptors in an image using::
 You can list all known standard descriptor names using::
 
    west bindesc list
+
+You can print the offset of the descriptors inside the image using::
+
+   west bindesc get_offset