Current documentation seems to only now go back as far as CC5.0.
The information you quote is contained in the Programming Guide for Cuda 8:
" 128-Bit Accesses: The majority of 128-bit accesses will cause 2-way bank conflicts, even if no two threads in a quarter-warp access different addresses belonging to the same bank. Therefore, to determine the ways of bank conflicts, one must add 1 to the maximum number of threads in a quarter-warp that access different addresses belonging to the same bank."