ARM: multi_v7_defconfig: Enable BRCMNAND driver

The Broadcom NAND driver is used by brcmstb, bcm63xx, bcm5301x and
Cygnus/iProc under mach-bcm, this is enough critical mass to enable it.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>