imximage: Add MX53 boot image support

This patch add the MX53 boot image support.

This patch has been tested on Freescale MX53EVK board
and MX51EVK board.

Signed-off-by: Jason Liu <r64343@freescale.com>
diff --git a/doc/README.imximage b/doc/README.imximage
index 3378f7e..c74239d 100644
--- a/doc/README.imximage
+++ b/doc/README.imximage
@@ -57,6 +57,13 @@
 2. Following are the valid command strings and associated data strings:-
 	Command string		data string
 	--------------		-----------
+	IMXIMAGE_VERSION        1/2
+				1 is for mx25/mx35/mx51 compatible,
+				2 is for mx53 compatible,
+				others is invalid and error is generated.
+				This command need appear the fist before
+				other valid commands in configuration file.
+
 	BOOT_FROM		nand/spi/sd/onenand
 				Example:
 				BOOT_FROM spi
@@ -69,8 +76,9 @@
 				Example (write to IOMUXC):
 				DATA 4 0x73FA88a0 0x200
 
-The processor support up to 60 register programming commands. An error
-is generated if more commands are found in the configuration file.
+The processor support up to 60 register programming commands for IMXIMAGE_VERSION 1
+and 121 register programming commands for IMXIMAGE_VERSION 2.
+An error is generated if more commands are found in the configuration file.
 
 3. All commands are optional to program.