how can i make one arria5 board to surpport opencl?

I haven't heard of anyone porting to Arria V but there isn't anything that binds OpenCL to any particular device family. I'm not expecting anyone to create a board support package for Arria V since Arria 10 has been announced but if there is a need for it a board vendor may address it.

Will altera give a reference design on how to port opencl to any particular device? The development board supporting opencl is too few.

There will be a Cyclone V SoC board package and porting it to Arria V SoC should be relatively straight forward. I don't know of plans for Altera to do this any time soon but it shouldn't be too difficult when the next release of the OpenCL SDK arrives.