doc: Tidy up and update part of the FIT documentation

This uses cfg instead of conf, and img instead of image. Fix these and
update in a few other places.

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

doc/uImage.FIT/source_file_format.txt

@@ -55,7 +55,7 @@ FIT is formally a flattened device tree (in the libfdt meaning), which
 conforms to bindings defined in this document.
 
 .its	- image tree source
-.itb	- image tree blob
+.fit	- flattened image tree blob
 
 c) Image building procedure
 
@@ -101,15 +101,15 @@ Root node of the uImage Tree should have the following layout:
     |
     o images
     | |
-    | o img@1 {...}
-    | o img@2 {...}
+    | o image@1 {...}
+    | o image@2 {...}
     | ...
     |
     o configurations
-      |- default = "cfg@1"
+      |- default = "conf@1"
       |
-      o cfg@1 {...}
-      o cfg@2 {...}
+      o conf@1 {...}
+      o conf@2 {...}
       ...
 
 
@@ -159,7 +159,7 @@ the '/images' node should have the following layout:
   - description : Textual description of the component sub-image
   - type : Name of component sub-image type, supported types are:
     "standalone", "kernel", "ramdisk", "firmware", "script", "filesystem",
-    "flat_dt".
+    "flat_dt" and others (see uimage_type in common/images.c).
   - data : Path to the external file which contains this node's binary data.
   - compression : Compression used by included data. Supported compressions
     are "gzip" and "bzip2". If no compression is used compression property
@@ -173,7 +173,8 @@ the '/images' node should have the following layout:
   - arch : Architecture name, mandatory for types: "standalone", "kernel",
     "firmware", "ramdisk" and "fdt". Valid architecture names are: "alpha",
     "arm", "i386", "ia64", "mips", "mips64", "ppc", "s390", "sh", "sparc",
-    "sparc64", "m68k", "microblaze", "nios2", "blackfin", "avr32", "st200".
+    "sparc64", "m68k", "microblaze", "nios2", "blackfin", "avr32", "st200",
+    "sandbox".
   - entry : entry point address, address size is determined by
     '#address-cells' property of the root node. Mandatory for for types:
     "standalone" and "kernel".