iommu/dmar: Reserve mmio space used by the IOMMU, if the BIOS forgets to

Intel-iommu initialization doesn't currently reserve the memory
used for the IOMMU registers. This can allow the pci resource
allocator to assign a device BAR to the same address as the
IOMMU registers. This can cause some not so nice side affects
when the driver ioremap's that region.

Introduced two helper functions to map & unmap the IOMMU
registers as well as simplify the init and exit paths.

Signed-off-by: Donald Dutile <ddutile@redhat.com>
Acked-by: Chris Wright <chrisw@redhat.com>
Cc: iommu@lists.linux-foundation.org
Cc: suresh.b.siddha@intel.com
Cc: dwmw2@infradead.org
Link: http://lkml.kernel.org/r/1338845342-12464-3-git-send-email-ddutile@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>