arm64: defconfig: Enable Samsung MFD and related configs

Exynos7 based espresso board uses S2MPS15, a multifunction device.
This patch enables S2MPS1X regulator, pmic-clk and rtc drivers utilized by
the same.

Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>