usb: dwc3: add Realtek DHC RTD SoC dwc3 glue layer driver

usb: dwc3: add Realtek DHC RTD SoC dwc3 glue layer driver

Realtek DHC RTD SoCs integrate dwc3 IP and has some customizations to
support different generations of SoCs.

The RTD1619b subclass SoC only supports USB 2.0 from dwc3. The driver
can set a maximum speed to support this. Add role switching function,
that can switch USB roles through other drivers, or switch USB roles
through user space through set /sys/class/usb_role/.

Signed-off-by: Stanley Chang <stanley_chang@realtek.com>
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/20230826031028.1892-1-stanley_chang@realtek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>