Fix X86 subtarget to not overwrite the autodetected features by calling InitMCProcessorInfo right after detecting them. Instead add a new function that only updates the scheduling model and call that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190919 91177308-0d34-0410-b5e6-96231b3b80d8