ARM: dts: imx6q-cm-fx6: Use the 'vpcie-supply' property

According to Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt,
the property for specifying the PCIe regulator is 'vpcie-supply', so
use the correct one.

Also fix the polarity of GPIO2_24 so that the regulator can operate
correctly.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Christopher Spinrath <christopher.spinrath@rwth-aachen.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>