arm: socfpga: mcvevk: Consolidate SDMMC environment

Remove the duplication of SDMMC environment configuration
from each boards' configuration header file into
socfpga_common.h

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>