dt-bindings: phy: uniphier-pcie: Add bindings for NX1 SoC

Update PCIe-PHY binding document for UniPhier NX1 SoC. Add a compatible
string for the SoC to the document.

Signed-off-by: Kunihiko Hayashi <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/phy/socionext,uniphier-pcie-phy.yaml

···
       - socionext,uniphier-pro5-pcie-phy
       - socionext,uniphier-ld20-pcie-phy
       - socionext,uniphier-pxs3-pcie-phy
+      - socionext,uniphier-nx1-pcie-phy
 
   reg:
     maxItems: 1