usb: dwc3-generic: support Qualcomm flattened DT

usb: dwc3-generic: support Qualcomm flattened DT

Qualcomm devicetrees are moving away from having a glue node with dwc3
as a subnode and now may just have a single flattened node.

Rockchip already have a glue_get_ctrl_dev op which returns the node for
the glue device itself, commonise this and reuse it for the new Qualcomm
node.

Lastly adjust the qscratch base address since it now requires an offset
from the dwc3 base.

Link: https://patch.msgid.link/20260116-casey-usb-role-switch-v2-1-83a1a6501a11@linaro.org
Signed-off-by: Casey Connolly <casey.connolly@linaro.org>