We discovered that on some devices even with iommu enabled
you can access all of system memory through the iommu translation.

Therefore, we revert the read method to the translation only service
and drop the write method completely.
Signed-off-by: NTom St Denis <tom.stdenis@amd.com>
Reviewed-by: NChristan König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>