Moved non-loop benchmarks to have suffix _cudnn

.../test/dnn_benchmarks/benchmarks/alexnet/alexnet_cudnn.cpp

...est/dnn_benchmarks/benchmarks/alexnet2/alexnet2_cudnn.cpp

...ks/benchmarks/alexnet_imagenet/alexnet_imagenet_cudnn.cpp

...n_benchmarks/benchmarks/lenet_mnist/lenet_mnist_cudnn.cpp

...t/dnn_benchmarks/benchmarks/mobilenet/mobilenet_cudnn.cpp

...est/dnn_benchmarks/benchmarks/resnet18/resnet18_cudnn.cpp

.../benchmarks/resnet50_imagenet/resnet50_imagenet_cudnn.cpp

...nchmarks/benchmarks/vgg16_cifar10/vgg16_cifar10_cudnn.cpp

...hmarks/benchmarks/vgg16_cifar100/vgg16_cifar100_cudnn.cpp

...hmarks/benchmarks/vgg16_imagenet/vgg16_imagenet_cudnn.cpp