AArch64: convert MC-layer test to .s file

The CodeGen aspects of this test are already covered by cfi-frame.ll;
making it an assembly file reduces the risk of incidental changes
affecting the test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180671 91177308-0d34-0410-b5e6-96231b3b80d8