[InferAddressSpaces] Add AS parameter to the pass factory

This enables the pass to be used in the absence of
TargetTransformInfo. When the argument isn't passed, the factory
defaults to UninitializedAddressSpace and the flat address space is
obtained from the TargetTransformInfo as before this change. Existing
users won't have to change.

Patch by Kevin Petit.

Differential Revision: https://reviews.llvm.org/D60602

llvm-svn: 359290