s-curves: 4xbanks version

s-curves: 4xbanks version

This version takes into account that the s-curve measurements
for M-26 test one bank (out of the four banks) at a time.
During the test of this one bank, the discriminator values of
the other banks is set to 255 (max).
The new version takes this into account assuming a certain
order of measuring the s-curves for banks A, B, C, D.