dt-bindings: arm: msm: Add child node entry for NTN3 i2c client

In order to access NTN3 switch registers add i2c client properties.
By accessing these registers root complex driver can toggle NTN3
GPIOs to tied to downstream endpoint reset. i2c interface is also
used to dump NTN3 registers for debugging PCIe link related issues.

Change-Id: I38279185c07a2ff7a9736a585f5e84053d459462