drm/amdgpu: change parameter passing in the VM code

Make it more flexible by passing src and page addresses
directly instead of the structures they contain.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>