Remove IsLittleEndian from TargetLowering and redirect to DataLayout

Summary:
This change is part of a series of commits dedicated to have a single
DataLayout during compilation by using always the one owned by the
module.

Reviewers: echristo

Subscribers: llvm-commits, rafael, yaron.keren

Differential Revision: http://reviews.llvm.org/D11017

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 241655