Remove FIXMEs in PPC test cases related to unaligned loads/stores

As pointed out by Bill in response to r177160, these two FIXMEs
can also be removed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177229 91177308-0d34-0410-b5e6-96231b3b80d8