drm/amdkfd: device pgmap owner at the svm migrate init

GPUs in the same XGMI hive have direct access to all
members'VRAM. When mapping memory to a GPU, we don't need
hmm_range_fault to fault device-private pages in the same
hive back to the host. Identifying the page owner as the hive,
rather than the individual GPU, accomplishes this.

Signed-off-by: Alex Sierra <alex.sierra@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>