LiveInterval: Distribute subregister liveranges to new intervals in ConnectedVNInfoEq...

LiveInterval: Distribute subregister liveranges to new intervals in ConnectedVNInfoEqClasses::Distribute()

This improves ConnectedVNInfoEqClasses::Distribute() to distribute the
segments and value numbers in the subranges instead of conservatively
clearing all subregister info.

No separate test here, just clearing the subrange instead of properly
distributing them would however break my upcoming fix regarding dead super
register definitions.

Differential Revision: http://reviews.llvm.org/D13075

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248334 91177308-0d34-0410-b5e6-96231b3b80d8