MAINTAINERS: Extend Samsung MFD drivers entry and add Krzysztof Kozlowski

Extend the entry for Samsung MFD drivers for PMIC devices (Power
Management Integrated Circuit) with bindings documentation, clock
(clk-s2mps11.c) and RTC drivers (rtc-s5m.c).

These PMIC devices are used on many Exynos-based boards like Arndale
Octa (S2MPS11), Gear 2 (S2MPS14).

Add Krzysztof Kozlowski as a supporter for reviewing them.
I am not the author of these drivers. However I have recently
contributed to most of them and I have access to datasheets and hardware.

Cc: Sangbeom Kim <sbkim73@samsung.com>
CC: Mike Turquette <mturquette@linaro.org>
CC: Stephen Boyd <sboyd@codeaurora.org>
CC: Alessandro Zummo <a.zummo@towertech.it>
CC: Alexandre Belloni <alexandre.belloni@free-electrons.com>
CC: Liam Girdwood <lgirdwood@gmail.com>
CC: Mark Brown <broonie@kernel.org>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>