vt-d: Remove the FLR logic in Xen.

vt-d: Remove the FLR logic in Xen.

The current simple logic has some issues: 1) Dstate transition is not
guaranteed to properly clear the device state; 2) the current code for
PCIe FLR is actually buggy: PCI_EXP_DEVSTA_TRPND doesn't mean the
completion of FLR; according to the PCIe spec, after issuing FLR, we
should wait at least 100ms.

The improved FLR logic will be added into xend.

Signed-off-by: Dexuan Cui <dexuan.cui@intel.com>