arm64: dts: imx8mp-skov-reva: Use hardware signal for SD card VSELECT

The USDHC controller is able to control the IO voltage of the SD card.
There is no reason to use a GPIO to control it.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
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Changes for v2:
* new patch