[ScopBuilder] Move addInvariantLoads to ScopBuilder. NFC.

Moved addInvariantLoads and functions listed below to ScopBuilder:
isAParameter
canAlwaysBeHoisted

These functions were referenced only by getNonHoistableCtx.

Moved CLI parameter PollyAllowDereferenceOfAllFunctionParams to
ScopBuilder.

Added iterator range through InvariantEquivClasses.

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

Differential Revision: https://reviews.llvm.org/D63172

llvm-svn: 363216