PCI: imx6: Move the imx6_pcie_ltssm_disable() earlier

Move the imx6_pcie_ltssm_disable() earlier and place it just behind the
imx6_pcie_ltssm_enable(), since it might not be only used by suspend
callback directly.

To be symmetric with imx6_pcie_ltssm_enable(), add the IMX6Q and IMX8MQ
switch cases in imx6_pcie_ltssm_disable().

Link: https://lore.kernel.org/r/1657783869-19194-17-git-send-email-hongxing.zhu@nxp.com
Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>