dt-bindings: PCI: uniphier-ep: Add bindings for NX1 SoC

Update PCI endpoint binding document for UniPhier NX1 SoC. Add a compatible
string, clock and reset lines for the SoC to the document.

Link: https://lore.kernel.org/r/1644480596-20037-2-git-send-email-hayashi.kunihiko@socionext.com


Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>