Description of the Feature:
Added a driver for SATA-controller of Intel processor with South Bridge, ICH-5, ICH-6 and ICH-7. 


Implementation:

1.	Code is divided in to two files. All functions, which are controller specific are kept in "drivers/ata_piix.c" file and functions, which are not controller specific, are kept in "common/cmd_sata.c" file.
2.	Reading and Writing from the SATA drive is done using PIO method.
3.	Driver can be configured for 48-bit addressing by defining macro CONFIG_LBA48, if this macro is not defined driver uses the 28-bit addressing.
4.	SATA read function is hooked to the File system, commands like ext2ls and ext2load file can be used. This has been tested.
5.	U-boot command "SATA_init" is added, which initializes the SATA controller and identifies the SATA drives connected to it.
6.	U-boot command "SATA" is added, which is used to read/write, print partition table and get info about the drives present. This I have implemented in same way as "ide" command is implemented in u-boot.
7.	This driver is for SATA in native mode.
8.	This driver does not support the Native command queuing and Hot-plugging.