As far as I know, there is no CUDA capable handheld GPU. However, there are a couple of implementations of OpenCL Embedded Profile (although I am not sure if they are publicly available) to make use of the mobile-GPUs for general computations. I have not studied the performance.
There are also a couple of small works that make use of OpenGL ES to perform some simple general tasks on the GPU (for example, grayscale conversion and LBP computations or image warpings), however the performance is not too high and the maximum speedups that you might find are in the order of 1.5X to 3X.