[ScopBuilder] Move getNonHoistableCtx to ScopBuilder. NFC.

This review is based on review: https://reviews.llvm.org/D62925 . It is
part of moving hoistInvariantLoads function and all functions referenced
only by hoistInvariantLoads to ScopBuilder.

Moved getNonHoistableCtx and functions listed below to ScopBuilder:
isRequiredInvariantLoad
hasNonHoistableBasePtrInScop
isAccessRangeTooComplex

These functions were referenced only by getNonHoistableCtx.

MaxDimensionsInAccessRange and MaxDisjunctsInDomain constant is marked
as extern and it is added to polly namespace. It is used by Scop and
ScopBuilder classes.

MaxDimensionsInAccessRange constant moved to ScopBuilder. It is not used
outside ScopBuilder.

Patch by Dominik Adamski <adamski.dominik@gmail.com>

Differential Revision: https://reviews.llvm.org/D63066

llvm-svn: 363214