The LDO28 is used only on Odroid XU3 for Display Port.  Define it so DTS
will describe entire hardware.

Depending on bootloader behavior this might affect the Display Port
because none of drivers are enabling it. By default it is off in S2MPS11
PMIC reset values.  However it could be enabled by bootloader so in such
case kernel will later disable it as unused regulator.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>