[PPCLoopDataPrefetch] Remove PPC from some of the names. NFC

This is done only to make the next patch that move the pass out PPC to
Transforms easier to read.  After this most line should show up as moved
lines in that patch.

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

llvm-svn: 261264