Add PHY2 register space to DT binding documentation.

We use minItems: 1 as DT update will come later and we don't
want warnings for existing DTs.

So far this register space was not required but due to the
newly identified Errata i2409 [1] we need to poke this
register space.

[1] https://www.ti.com/lit/er/sprz487d/sprz487d.pdfSigned-off-by: Roger Quadros <rogerq@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240214-for-v6-9-am62-usb-errata-3-0-v3-4-147ec5eae18c@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>