[FastISel][AArch64] Extend floating-point materialization test.

This adds the missing test that I promised for r215753 to test the
materialization of the floating-point value +0.0.

Related to <rdar://problem/18027157>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216019 91177308-0d34-0410-b5e6-96231b3b80d8