configs: remove empty #ifdef block from mv-common.h

The last option guarded by this ifdef was removed in commit 68d53420
("sf: Move SPI flash drivers to defconfig"). Remove the now empty
ifdef/endif block and the associated comment.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>