Add extra CUDA flags.

On Felice request, I forced code generation for the current nVidia
architecture. I assume in any case we will never use anything lower than
this, so I guess it's fine.
Merge pull request #737 from ktf/fix-cuda-options

Fix cuda options
Merge remote branch 'origin/IB/CMSSW_7_1_X/stable' into IB/CMSSW_7_0_X/stable