[TargetSchedule] shrink interface for init(); NFCI

The TargetSchedModel is always initialized using the TargetSubtargetInfo's 
MCSchedModel and TargetInstrInfo, so we don't need to extract those and 
pass 3 parameters to init().

Differential Revision: https://reviews.llvm.org/D44789


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329540 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed