PCI: imx6: Enable PHY internal regulator when supplied >3V

The i.MX8MQ PCIe PHY needs 1.8V in default but can be supplied by either a
1.8V or a 3.3V regulator.

The "vph-supply" DT property tells us which external regulator supplies the
PHY. If that regulator supplies anything over 3V, enable the PHY's internal
3.3V-to-1.8V regulator.

Link: https://lore.kernel.org/r/1622771269-13844-3-git-send-email-hongxing.zhu@nxp.com


Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>