*** Add ext4 filesystem support in uboot ***

***
This patch series adds support for ext4 ls,load and write features in uboot Journaling is supported for write feature.

To Enable ext2 ls and load commands, modify the board specific config file with #define CONFIG_CMD_EXT2

To Enable ext4 ls and load commands, modify the board specific config file with #define CONFIG_CMD_EXT4

To enable ext4 write command, modify the board specific config file with #define CONFIG_CMD_EXT4
#define CONFIG_CMD_EXT4_WRITE

Steps to test:

1. After applying the patch, ext4 specific commands can be seen in the boot loader prompt using
UBOOT #help

ext4load- load binary file from a Ext4 file system ext4ls - list files in a directory (default /) ext4write- create a file in ext4 formatted partition

2. To list the files in ext4 formatted partition, execute ext4ls <interface> <dev[:part]> [directory] For example:
UBOOT #ext4ls mmc 0:5 /usr/lib

3. To read and load a file from an ext4 formatted partition to RAM, execute ext4load <interface> <dev[:part]> [addr] [filename] [bytes] For example:
UBOOT #ext4load mmc 2:2 0x30007fc0 uImage

4. To write a file to a ext4 formatted partition.
a) First load a file to RAM at a particular address for example 0x30007fc0. Now execute ext4write command
ext4write <interface> <dev[:part]> [filename] [Address] [sizebytes] For example:
UBOOT #ext4write mmc 2:2 /boot/uImage 0x30007fc0 6183120
(here 6183120 is the size of the file to be written)
Note: Absolute path is required for the file to be written

***