[PowerPC 4/4] Enable little-endian support for VSX.

With the foregoing three patches, VSX instructions can be used for
little endian.  This patch removes the restriction that prevented
this, and re-enables the test cases from the first three patches.





git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223792 91177308-0d34-0410-b5e6-96231b3b80d8