ARM: exynos_defconfig: Enable Panfrost and Lima drivers

Enable support for Mali GPU with Panfrost and Lima drivers.  Most of
Exynos chipsets come with Mali GPUs:
1. Mali 400 (Exynos3250, Exynos4210, Exynos4412),
2. Mali T628 (Exynos542x).

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>