[AArch64] Add the scheduling model for Exynos-M1

Summary:
Add the core scheduling model for the Samsung Exynos-M1 (ARMv8-A).


Reviewers: jmolloy, rengolin, christof, MinSeongKIM, t.p.northover

Subscribers: aemerson, rengolin, MatzeB

Differential Revision: http://reviews.llvm.org/D16644

llvm-svn: 259958