dt-bindings: phy: Add imx8 pcie phy driver support

Add dt-binding for the standalone i.MX8 PCIe PHY driver.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Tim Harvey <tharvey@gateworks.com>
Tested-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1638432158-4119-3-git-send-email-hongxing.zhu@nxp.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>