If you have already generated a displacement map, you can create a bump map from it (which seems to be Unity's closest equivalent). If you have a hi-poly model and you need to create a displace map from it, that's more of a Max/Maya question and you may need to Google it. I find there is often some confusion on the map terms between different 3D programs. As I understand them;

Bump Map : greyscale image mapping high to low on a model, affects lighting only.

Displace Map : greyscale image mapping high to low, but displaces vertices on a poly surface (some fancy shaders do this through other means, but the idea is that the outline and definition changes)

Normal Map : colour image mapping perpendicular tangents ("normals") of a surface.

Unity's Bump Map actually appears to be a Normal map, but generated from a greyscale image. If you are using a displace or bump map in Maya, try importing it into Unity and then (in the texture inspector) ticking 'generate bump map' then apply. It should turn crazy colours in the view (this is now a Normal Map).

Then set your object's material to "Bumped Diffuse". Place your diffuse texture in the first slot and the newly imported bump map to the second. This should hopefully give you the desired effect!

But this is not a displacement map... The Bumped Diffuse shader only uses the normal map. It is not the same.

Unity doesn't support displacement map, I have search for an asset in the store and I think it has not been created yet.

Please refer to http://answers.unity3d.com/questions/411800/maya-fbx-does-it-contain-displacement-maps.html#answer-411921

For further info on Displacement support