Also exports two functions that vendor drivers can call
to trace DMA mappings.  This is meant to help translate
IOMMU mappings of bus addresses back to physical pages.

Used by the umr amdgpu debugger for instance.
Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

(v2): Use dev_name() to get PCI path instead.
(v3): Use correct types for dma/phys addresses