<XCM> Cu and GNR wire param functions now check min pitch first

This ensures we use the lowest pitch we can actually get away with, and
ensures that checks based on the min pitch later on will function
correctly. Previously, since the new CU/CUREP/GNR wire param functions
used a binary search bounded at the min pitch, but never actually
checked the min pitch, wires could never actually be assigned the
minimum pitch, just arbitrarily close to it (depending on the number of
binary search generations allowed).