[ValueTracking] Use KnownOnes to provide a better bound on known zeros for ctlz/cttz intrinics

This patch uses KnownOnes of the input of ctlz/cttz to bound the value that can be returned from these intrinsics. This makes these intrinsics more similar to the handling for ctpop which already uses known bits to produce a similar bound.

Differential Revision: https://reviews.llvm.org/D32521

llvm-svn: 302444