drm/amdgpu: add svm_bo eviction to enable_signal cb

Add to amdgpu_amdkfd_fence.enable_signal callback, support
for svm_bo fence eviction.

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