pci: imx: Add iMX6SX compatible

The driver works fine with iMX6SX, add the missing compatible string.
Signed-off-by: NMarek Vasut <marex@denx.de>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>

drivers/pci/pcie_imx.c

@@ -815,6 +815,7 @@ static const struct dm_pci_ops imx_pcie_ops = {
 
 static const struct udevice_id imx_pcie_ids[] = {
 	{ .compatible = "fsl,imx6q-pcie" },
+	{ .compatible = "fsl,imx6sx-pcie" },
 	{ }
 };