usb: cdns3: imx: fix can't create core device the second time issue

The cdns3 core device is populated by calling of_platform_populate,
the flag OF_POPULATED is set for core device node, if this flag
is not cleared, when calling of_platform_populate the second time
after loading parent module again, the OF code will not try to create
platform device for core device.

To fix it, it uses of_platform_depopulate to depopulate the core
device which the parent created, and the flag OF_POPULATED for
core device node will be cleared accordingly.

Cc: <stable@vger.kernel.org>
Fixes: 1e056efa ("usb: cdns3: add NXP imx8qm glue layer")
Signed-off-by: Peter Chen <peter.chen@nxp.com>