[InstCombine] Pass the DominatorTree, AssumptionCache, and context instruction to a few calls to isKnownPositive, isKnownNegative, and isKnownNonZero

Every other place in InstCombine that uses these methods in ValueTracking already pass this information. This makes the remaining sites consistent.

Differential Revision: https://reviews.llvm.org/D33567

llvm-svn: 304018