powerpc/85xx: Add QE USB support for MPC8569E-MDS boards

- Add gpio-controller node for BCSR17, it is used to control USB
  speed and VBUS;
- Add timer node for QE GTM, needed for USB host;
- Add usb node itself;
- Add some probing code for BCSR GPIOs.

NOTE: QE USB doesn't work on prototype boards, but should work on
      pilot boards if specs and schematics are correct, though we
      don't have the pilot boards to actually test it.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>