arm: mvebu: db-mv784mp-gp: Enable common file-system support

This patch adds the common FS options to the Marvell AXP eval board. This
includes EXT2, EXT4, FAT and VFAT. And of course the generic FS commands.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>