dev-util/nvidia-cuda-sdk: add version 6.5.11

Adapted the cuda 6.0.37 sdk ebuild for the 6.5.11 release
candidate version. The package is fetch restricted to give the
user a hint where to get the cuda*.run files, which are only
available to registered cuda developers.

The ~x86 flag was removed, because the CUDA samples and
some sientific libraries are longer provided by NVIDIA for
x86-based linux distributions.