Use less CPU worker if GPU are used

Benchmark/axpy/axpy.cpp

Benchmark/cholesky_gemm/cholesky-mpi.cpp

Benchmark/cholesky_gemm/cholesky.cpp

Benchmark/cholesky_gemm/gemm-mpi.cpp

Benchmark/cholesky_gemm/gemm.cpp

Benchmark/particles/particles-simu.cpp

Src/Compute/SpWorkerTeamBuilder.hpp