[mips][msa] Merge basic_operations_little.ll into basic_operations.ll.

Now that FileCheck supports multiple check prefixes, we don't need to keep the
little and big endian versions of this test separate anymore. Merge them back
together.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194826 91177308-0d34-0410-b5e6-96231b3b80d8