ARM: dts: imx6sx-softing-vining-2000: Enable PCI support

Add PCI support.

Since this board has an active high PCI reset line, pass the
'reset-gpio-active-high' property.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Tested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>