usb: dwc3: Add dwc3 glue driver for am62

Add glue code for TI AM62 to the dwc3 driver; Most code adopted from
TI vendor u-boot code.

Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # on beagle play