R600/SI: Add a lower case alias for subtarget feature: +DumpCode
R600/SI: Add a lower case alias for subtarget feature: +DumpCode

llc converts all feature strings to lower case, while the LLVM C API
does not, so we need a lower case alias in order to test this with llc.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@236003 91177308-0d34-0410-b5e6-96231b3b80d8

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