usb: dwc3: core: Expose core driver as library

The DWC3 IP block is handled by three distinct device drivers: XHCI,
DWC3 core and a platform specific (optional) DWC3 glue driver.

This has resulted in, at least in the case of the Qualcomm glue, the
presence of a number of layering violations, where the glue code either
can't handle, or has to work around, the fact that core might not probe
deterministically.

An example of this is that the suspend path should operate slightly
different depending on the device operating in host or peripheral mode,
and the only way to determine the operating state is to peek into the
core's drvdata.

The Qualcomm glue driver is expected to make updates in the qscratch
register region (the "glue" region) during role switch events, but with
the glue and core split using the driver model, there is no reasonable
way to introduce listeners for mode changes.

Split the dwc3 core platform_driver callbacks and their implementation
and export the implementation, to make it possible to deterministically
instantiate the dwc3 core as part of the dwc3 glue drivers and to
allow flattening of the DeviceTree representation.

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-v7-3-f015b358722d@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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