Revert "[ARM] Remove XFAIL on test/CodeGen/Generic/MachineBranchProb.ll"

Summary:
This reverts commit 79c37e1a4ff1e634da8f95322f080601b4c815fc.
    
    This test passes locally but fails on the community buildbot. So we will let it
    XFAIL for now.

Patched by Mandeep Singh Grang (mgrang@codeaurora.org)

Reviewers: kparzysz, weimingz

Subscribers: aemerson, rengolin, llvm-commits

Differential Revision: http://reviews.llvm.org/D14189

llvm-svn: 251664