dm: sf: Add Atmel DataFlash spi flash driver

Atmel DataFlash chips have commands different from common spi
flash commands.
Atmel DataFlash also have special page-size.
This driver add support for accessing Atmel DataFlash.
It is based on the Driver Model.
Example:
=> sf probe 1:0
SPI DataFlash: Detected AT45DB021B with page size 264 Bytes, erase size 264 Bytes, total 264 KiB, revision d
=> sf erase 0 42000
SF: 270336 bytes @ 0x0 Erased: OK
=> mw.l 82000000 45444342 20000
=> sf write 82000000 0 42000
SF: 270336 bytes @ 0x0 Written: OK
=> sf read 83000000 0 42000
SF: 270336 bytes @ 0x0 Read: OK
=> cmp.b 82000000 83000000 42000
Total of 270336 byte(s) were the same

Signed-off-by: Haikun Wang <haikun.wang@freescale.com>
Tested-by: Haikun Wang <haikun.wang@freescale.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Chakra Divi <cdivi@openedev.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>