Revert r158679 - use case is unclear (and it increases the memory footprint).

Revert r158679 - use case is unclear (and it increases the memory footprint).

Original commit message:
    Allow up to 64 functional units per processor itinerary.

    This patch changes the type used to hold the FU bitset from unsigned to uint64_t.
    This will be needed for some upcoming PowerPC itineraries.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159027 91177308-0d34-0410-b5e6-96231b3b80d8