R600/SI: Restore PrivateGlobalPrefix to the default ELF value of ".L"

This was changed in r223323.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223579 91177308-0d34-0410-b5e6-96231b3b80d8
Reformat.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223580 91177308-0d34-0410-b5e6-96231b3b80d8