arm: multi_v7_defconfig: Enable initrd/initramfs support

Add CONFIG_BLK_DEV_INITRD to the defconfig to support
initramfs and initrd.
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/configs/multi_v7_defconfig

 CONFIG_EXPERIMENTAL=y
 CONFIG_NO_HZ=y
 CONFIG_HIGH_RES_TIMERS=y
+CONFIG_BLK_DEV_INITRD=y
 CONFIG_ARCH_MVEBU=y
 CONFIG_MACH_ARMADA_370=y
 CONFIG_ARCH_SIRF=y