OMAP3: Fix missing GPMC_CONFIG_CS0_BASE

Applying two indepenent OMAP3 patches resulted in missing
GPMC_CONFIG_CS0_BASE. Patch "omap3: embedd gpmc_cs into gpmc
config struct" removes GPMC_CONFIG_CS0_BASE, independent patch
"omap3: bug fix for NOR boot support" introduces it's usage.
Re-introduce GPMC_CONFIG_CS0_BASE.

Signed-off-by: Dirk Behme <dirk.behme@googlemail.com>