usb: dwc3-generic: Export glue structures and functions

usb: dwc3-generic: Export glue structures and functions

In order to allow external SoC-dependent glue drivers to use dwc3-generic
functions, push the glue structures and export the functions to a header
file.

The exported structures and functions are:

- struct dwc3_glue_data
- struct dwc3_glue_ops
- dwc3_glue_bind()
- dwc3_glue_probe()
- dwc3_glue_remove()

The SoC-dependent glue drivers can only define their own wrapper driver
and specify these functions. The drivers can also add their own compatible
strings and configure functions.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Marek Vasut <marex@denx.de>