amd-iommu: flush domain tlb when attaching a new device

When kexec'ing to a new kernel (for example, when crashing and launching
a kdump session), the AMD IOMMU may have cached translations.  The kexec'd
kernel, during initialization, will invalidate the IOMMU device table
entries, but not the domain translations.  These stale entries can cause
a device's DMA to fail, makes it rough to write a dump to disk when the
disk controller can't DMA ;-)

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>