The saturation instructions appeared in v6T2, with DSP extensions, but they
were being accepted / generated on any, with the new introduction of the
saturation detection in the back-end. This commit restricts the usage to
DSP-enable only cores.
Fixes PR28607.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276701 91177308-0d34-0410-b5e6-96231b3b80d8