DWC USB3 DT node is supposed to be compliant with the Generic xHCI
Controller schema, but with additional vendor-specific properties, the
controller-specific reference clocks and PHYs. So let's convert the
currently available legacy text-based DWC USB3 bindings to the DT schema
and make sure the DWC USB3 nodes are also validated against the
usb-xhci.yaml schema.

Note 1. we have to discard the nodename restriction of being prefixed with
"dwc3@" string, since in accordance with the usb-hcd.yaml schema USB nodes
are supposed to be named as "^usb(@.*)".

Note 2. The clock-related properties are marked as optional to match the
DWC USB3 driver expectation and to improve the bindings mainainability
so in case if there is a glue-node it would the responsible for the
clocks initialization.

Signed-off-by: Serge Semin <redacted>

---

Changelog v2:
- Discard '|' from the descriptions, since we don't need to preserve
  the text formatting in any of them.
- Drop quotes from around the string constants.
- Fix the "clock-names" prop description to be referring the enumerated
  clock-names instead of the ones from the Databook.

Changelog v3:
- Apply usb-xhci.yaml# schema only if the controller is supposed to work
  as either host or otg.

Changelog v4:
- Apply usb-drd.yaml schema first. If the controller is configured
  to work in a gadget mode only, then apply the usb.yaml schema too,
  otherwise apply the usb-xhci.yaml schema.
- Discard the Rob'es Reviewed-by tag. Please review the patch one more
  time.

Changelog v5:
- Add "snps,dis-split-quirk" property to the DWC USB3 DT schema.
- Add a commit log text about the clock-related property changes.
- Make sure dr_mode exist to apply the USB-gadget-only schema.
---
 .../devicetree/bindings/usb/dwc3.txt          | 128 -------
 .../devicetree/bindings/usb/snps,dwc3.yaml    | 312 ++++++++++++++++++
 2 files changed, 312 insertions(+), 128 deletions(-)
 delete mode 100644 Documentation/devicetree/bindings/usb/dwc3.txt
 create mode 100644 Documentation/devicetree/bindings/usb/snps,dwc3.yaml

diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
deleted file mode 100644
index 1aae2b6160c1..000000000000
--- a/Documentation/devicetree/bindings/usb/dwc3.txt
+++ /dev/null

@@ -1,128 +0,0 @@
-synopsys DWC3 CORE
-