Marvell Sheevaplug Board support

Reference:
http://plugcomputer.org/
http://openplug.org/plugwiki/index.php/Das_U-boot_plug_support



This patch is tested for-
1. Boot from DRAM/NAND flash
2. File transfer using tftp
3. NAND flash read/write/erase
4. Linux kernel and RFS Boot from NAND
5. Enabled USB PHY init for kernel need
6. Boot from USB supported

Note: to boot Kirkwood kernel with USB support,
	you should add "usb start" in the boot sequence

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>