ARM: meson: switch AXG & GX dwc2 otg to DM

ARM: meson: switch AXG & GX dwc2 otg to DM

With CONFIG_DM_USB_GADGET=y, we no longer need any board_usb_*() logic
because:
* the dwc2 driver is DM compatible, and handles its own clock enabling
* the dwc3-meson-gxl glue drivers handles "force mode switching"

Remove all mach-meson gx & axg usb code and enable CONFIG_DM_USB_GADGET.

Note: Only configs having both CONFIG_USB_DWC3_MESON_GXL=y *and*
      USB_GADGET_DWC2_OTG=y have been updated.

Thanks for the original work from Mattijs at [1]

[1] https://lore.kernel.org/all/20221024-meson-dm-usb-v1-2-2ab077a503b9@baylibre.com/

Reviewed-by: Mattijs Korpershoek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Neil Armstrong <[email protected]>