add option to specify CUDA arch

[cydrain]

Please state you issue using the following template and, most importantly, in English.

Is your feature request related to a problem? Please describe.
GPU FAISS building is timing consuming, if we only build GPU FAISS with specified CUDA arch,
we can save a lot of building time.

Describe the solution you'd like
Add an option in build.sh to specify the CUDA arch we can support.
Proposal 1) add option "-cuda-arch=-gencode=arch=compute_61,code=sm_61 -gencode=arch=compute_75,code=sm_75"
Proposal 2) add option "-ci_only=true"
without above options, 4 CUDA arch will be specified.