sf: Add SPI protection mechanism from the kernel

Add the SPI NOR protection mechanism from the kernel.

This code is based on the work from
Brian Norris <computersforpeace@gmail.com>
Here is the commit details:
"mtd: spi-nor: refactor block protection functions"
(sha1: 62593cf40b23b523b9fc9334ca61ba6c595ebb09)

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Jagan Teki <jteki@openedev.com>

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>