vtd: fix Dom0 S3 when VT-d is enabled.

vtd: fix Dom0 S3 when VT-d is enabled.

On some platforms that support Queued Invalidation and Interrupt
Remapping, Dom0 S3 doesn't work. The patch fixes the issue.

1) In device_power_down(), we should invoke iommu_suspend() after
ioapic_suspend(); in device_power_up(), we should invoke
iommu_resume() before ioapic_resume().

2) Add 2 functions: disable_qinval() and disable_intremap(); in
iommu_suspend(), we invoke them and iommu_disable_translation().
   Rename qinval_setup() to enable_qinval() and rename
   intremap_setup() to enable_intremap().

3) In iommu_resume(), remove the unnecessary
iommu_flush_{context, iotlb}_global() -- actually we mustn't do that
if Queued Invalidation was enabled before S3 because at this point of
S3 resume, Queued Invalidation hasn't been re-enabled.

4) Add a static global array ioapic_pin_to_intremap_index[] to
remember what intremap_index an ioapic pin uses -- during S3 resume,
ioapic_resume() re-writes all the ioapic RTEs, so we can use the array
to re-use the previously-allocated IRTE;

5) Some cleanups:
   a) Change some failure handlings in enable_intremap() to panic().
   b) Remove the unnecessary local variable iec_cap in
   __iommu_flush_iec().
   c) Add a dmar_writeq(iommu->reg, DMAR_IQT_REG, 0) in
   enable_qinval().

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