ARM: dts: exynos: Define vqmmc for SD card and allow disabling regulators on Odroid X/X2/U3

The SD-card vmmc-supply contained incorrectly two regulators. The second
one is ignored. Fix this by defining proper vmmc and vqmmc supplies.
Additionally these regulators do not have to be always on, so allow
disabling them to reduce energy consumption.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>