cosmetic: uImage.FIT: fix documents

- Fix the path to source_file_format.txt
  - Fix a minor typo
  - Fix the type for FIT blob: it must be "flat_dt"

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

doc/uImage.FIT/howto.txt

@@ -20,8 +20,8 @@ www.jdl.com for its latest version. mkimage (together with dtc) takes as input
 an image source file, which describes the contents of the image and defines
 its various properties used during booting. By convention, image source file
 has the ".its" extension, also, the details of its format are given in
-doc/source_file_format.txt. The actual data that is to be included in the
-uImage (kernel, ramdisk, etc.) is specified in the image source file in the
+doc/uImage.FIT/source_file_format.txt. The actual data that is to be included in
+the uImage (kernel, ramdisk, etc.) is specified in the image source file in the
 form of paths to appropriate data files. The outcome of the image creation
 process is a binary file (by convention with the ".itb" extension) that
 contains all the referenced data (kernel, ramdisk, etc.) and other information
@@ -39,7 +39,7 @@ Here's a graphical overview of the image creation and booting process:
 
 image source file     mkimage + dtc		  transfer to target
 	+	     ---------------> image file --------------------> bootm
-image data files(s)
+image data file(s)
 
 
 Example 1 -- old-style (non-FDT) kernel booting

doc/uImage.FIT/source_file_format.txt

@@ -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",
-    "fdt".
+    "flat_dt".
   - 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