x86: Move pci_iommu_init to rootfs_initcall()

We want this to happen after the PCI quirks, which are now running at
the very end of the fs_initcalls.

This works around the BIOS problems which were originally addressed by
commit db8be50c4307dac2b37305fc59c8dc0f978d09ea ('USB: Work around BIOS
bugs by quiescing USB controllers earlier'), which was reverted in
commit d93a8f829fe1d2f3002f2c6ddb553d12db420412.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

arch/x86/kernel/pci-dma.c

@@ -311,7 +311,7 @@ void pci_iommu_shutdown(void)
 	amd_iommu_shutdown();
 }
 /* Must execute after PCI subsystem */
-fs_initcall(pci_iommu_init);
+rootfs_initcall(pci_iommu_init);
 
 #ifdef CONFIG_PCI
 /* Many VIA bridges seem to corrupt data for DAC. Disable it here */