x86, swiotlb: Make SWIOTLB use IOMMU_INIT_* macros.

We utilize the IOMMU_INIT macros to create this dependency:

       [pci_xen_swiotlb_detect]
                 |
       [pci_swiotlb_detect_override]
                 |
       [pci_swiotlb_detect_4gb]

And set the SWIOTLB IOMMU_INIT to utilize 'pci_swiotlb_init'
for .init and 'pci_swiotlb_late_init' for .late_init.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
LKML-Reference: <1282845485-8991-6-git-send-email-konrad.wilk@oracle.com>
CC: Fujita Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>