Enabling the support of storing U-Boot environment
within serial NOR flash. By default, its still
store into SDMMC

Signed-off-by: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Dinh Nguyen <dinh.linux@gmail.com>
Cc: Pavel Machek <pavel@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Stefan Roese <sr@denx.de>