overlays: Add Pi 5 version of dwc2

Most bus masters on Pi 5 have access to at least the lower 4GB, but
the old DWC OTG controller is still restricted to the first 1GB.
Create a Pi 5-specific version of the overlay including a fragment
that ensures the swiotlb bounce buffers are allocated in that
area.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>