ARM: multi_v7_defconfig: Build ChromeOS EC drivers as modules

Since the multi_v7_defconfig is used to build an image for different
platforms, the options should be enabled as module whenever possible.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>