Update necessary for the new version of CUDA.jl

[BoundaryValueProblems]

With CUDA.jl v5.5.0 and above, the following part in src/Utils.jl does not work anymore. I asked the question on CUDA.jl: JuliaGPU/CUDA.jl#2509 and please see what @maleadt said there. He also suggested looking at the following pull request: https://github.com/JuliaGPU/CUDA.jl/pull/2430/files
Here are the two functions need to be changed or perhaps removed?

# TODO this is somewhat kludgy, not sure why cu was converting these back
function CUDA.cu(P::FFTW.rFFTWPlan)
    return plan_rfft(cu(zeros(real(eltype(P)), P.sz)), P.region)
end
CUDA.cu(P::CUFFT.rCuFFTPlan) = P

function CUDA.cu(P::FFTW.cFFTWPlan)
    return plan_fft(cu(zeros(eltype(P), P.sz)), P.region)
end
CUDA.cu(P::CUFFT.cCuFFTPlan) = P

Thanks!