usb: dwc3: pci: rely on default PM callbacks from PCI driver utility

There is nothing specific being done in the suspend and
resume callbacks that is not already taken care of in PCI
driver core, so dropping the functions.

Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>