Impact: fix boot crash on AMD IOMMU if CONFIG_GART_IOMMU is off

Currently these macros evaluate to a no-op except the kernel is compiled
with GART or Calgary support. But we also need these macros when we have
SWIOTLB, VT-d or AMD IOMMU in the kernel. Since we always compile at
least with SWIOTLB we can define these macros always.

This patch is also for stable backport for the same reason the SWIOTLB
default selection patch is.
Signed-off-by: NJoerg Roedel <joerg.roedel@amd.com>
Cc: <stable@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>