soc/qman: test: Don't use dummy platform device for dma mapping

Replace dummy platform device hack with a reference to a portal's
platform device, in order to dma map the test frame for this
small unit test.  The 2 qman symbols need to be exported because
this self test is a kernel module.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Scott Wood <oss@buserror.net>