ARM: dts: exynos: Define vqmmc for eMMC card on Odroid X/X2/U3

The eMMC card vmmc-supply contained incorrectly two regulators: LDO20
and buck8. The second one is ignored. Additionally the buck8 is a vqmmc
supply only on X and X2. On U3 the buck8 is providing power to the LAN
(SMSC95xx) so instead the LDO22 should be used.

Fix this by defining proper vmmc and vqmmc supplies for respective
boards.

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