Revert "drm/amdkfd: process_info lock not needed for svm"

This reverts commit 3abfe30d.

To fix deadlock in kFDSVMEvictTest when xnack off.

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>