drm/amdkfd: new range accessible by all GPUs

If xnack is on, new range is created to recover retry vm fault or
created by SVM API calls, set all GPUs have access to the range.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>