Add driver for S-ATA-controller on Intel processors with South

Add driver for S-ATA-controller on Intel processors 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 S-ATA 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. S-ATA 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 S-ATA
   controller and identifies the S-ATA 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 S-ATA in native mode.

8. This driver does not support the Native command queuing and
   Hot-plugging.

Signed-off-by: Mushtaq Khan <mushtaq_k@procsys.com>