Add SPI NOR support:

=> sf probe
SF: Detected SST25VF032B with page size 256 Bytes, erase size 4 KiB, total 4 MiB

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com>