[GISel]: Add GISelKnownBits analysis

[GISel]: Add GISelKnownBits analysis

https://reviews.llvm.org/D65698

This adds a KnownBits analysis pass for GISel. This was done as a
pass (compared to static functions) so that we can add other features
such as caching queries(within a pass and across passes) in the future.
This patch only adds the basic pass boiler plate, and implements a lazy
non caching knownbits implementation (ported from SelectionDAG). I've
also hooked up the AArch64PreLegalizerCombiner pass to use this - there
should be no compile time regression as the analysis is lazy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@368065 91177308-0d34-0410-b5e6-96231b3b80d8