Add prox_sp GPU2 implementation with gpu_mod@422d2d79 and a test/benchmark (test_prox_sp_gpu).

gpu_mod

misc/test/CMakeLists.txt

misc/test/src/C++/test_prox_sp_gpu.cpp.in

src/faust_linear_operator/GPU2/faust_MatDense_gpu.cpp.in

src/faust_linear_operator/GPU2/faust_MatDense_gpu.h

src/faust_linear_operator/GPU2/faust_prox_gpu.h

src/faust_linear_operator/GPU2/faust_prox_gpu.hpp