dt-bindings: regulator/clock/mfd: Reorganize S2MPS-family bindings

Bindings for Samsung S2M and S5M family PMICs are in mess. They are
spread over different files and subdirectories in a non-consistent way.
The devices and respective drivers for them share a lot in common so
everything could be organized in a more readable way.

Reorganize the S2MPS11/13/14/15 Device Tree bindings to match the
drivers for this family of devices:
 - move mfd/s2mps11.txt to mfd/samsung,sec-core.txt for the main MFD
   driver (common for entire family),
 - split clock block to clock/samsung,s2mps11.txt,
 - split regulator block to regulator/samsung,s2mps11.txt.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Acked-by: Michael Turquette <mturquette@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>