[TTI] Add getPrefetchDistance from PPCLoopDataPrefetch, NFC

This patch is part of the work to make PPCLoopDataPrefetch
target-independent
(http://thread.gmane.org/gmane.comp.compilers.llvm.devel/92758).

As it was discussed in the above thread, getPrefetchDistance is
currently using instruction count which may change in the future.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258995 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed