dt-bindings: mt8173-xhci: support host side of dual-role mode
Some resources, such as IPPC register etc, shared with device
driver are moved into common glue layer when xHCI driver is the
host side of dual-role mode and they should be changed as optional
properties if they are required ones before. For clarity, add
a new part of binding to support host side of dual-role mode.
Additionally add optional properties of pinctrl for host only mode