arm64: configs: Enable PCIe support for imx8mq boards

Enable PCI_IMX6 to get PCI support for imx8mq boards like imx8mq-evk,
imx8mq-kontron-pitx-imx8m and imx8mq-zii-ultra.

The driver only has build-in support and cannot be compiled as module.
Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/configs/defconfig

@@ -225,6 +225,7 @@ CONFIG_PCI_HOST_THUNDER_PEM=y
 CONFIG_PCI_HOST_THUNDER_ECAM=y
 CONFIG_PCIE_ROCKCHIP_HOST=m
 CONFIG_PCIE_BRCMSTB=m
+CONFIG_PCI_IMX6=y
 CONFIG_PCI_LAYERSCAPE=y
 CONFIG_PCIE_LAYERSCAPE_GEN4=y
 CONFIG_PCI_HISI=y