usb: dwc3: qcom: Transition to flattened model

The USB IP-block found in most Qualcomm platforms is modelled in the
Linux kernel as 3 different independent device drivers, but as shown by
the already existing layering violations in the Qualcomm glue driver
they can not be operated independently.

With the current implementation, the glue driver registers the core and
has no way to know when this is done. As a result, e.g. the suspend
callbacks needs to guard against NULL pointer dereferences when trying
to peek into the struct dwc3 found in the drvdata of the child.
Even with these checks, there are no way to fully protect ourselves from
the race conditions that occur if the DWC3 is unbound.

Missing from the upstream Qualcomm USB support is handling of role
switching, in which the glue needs to be notified upon DRD mode changes.
Several attempts has been made through the years to register callbacks
etc, but they always fall short when it comes to handling of the core's
probe deferral on resources etc.

Moving to a model where the DWC3 core is instantiated in a synchronous
fashion avoids above described race conditions.

It is however not feasible to do so without also flattening the
DeviceTree binding, as assumptions are made in the DWC3 core and
frameworks used that the device's associated of_node will the that of
the core. Furthermore, the DeviceTree binding is a direct
representation of the Linux driver model, and doesn't necessarily
describe "the USB IP-block".

The Qualcomm DWC3 glue driver is therefor transitioned to initialize and
operate the DWC3 within the one device context, in synchronous fashion.

To provide a limited time backwards compatibility, a snapshot of the
driver is retained in a previous commit. As such no care is taken in the
dwc3-qcom driver for the qcom,dwc3 backwards compatibility.

Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-QRD
Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250414-dwc3-refactor-v7-6-f015b358722d@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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