ARM: exynos_defconfig: Enable SquashFS and increase RAM block device size

All modules built from exynos_defconfig occupy about 55M, so enable
squashfs filesystem support and increase default ram block device size
to 32M to enable deploying them on initrd. Such initrd, using squashfs
requires at least 24M.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>