Various small changes related to the Condition Register on PowerPC.

Various small changes related to the Condition Register on PowerPC.

Don't spill to the CR save area when using the SVR4 ABI for now.
Don't rely on constants assigned for registers to be in order (they aren't assigned in order).
Make sure CR bits are mapped to the corresponding CR field.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74767 91177308-0d34-0410-b5e6-96231b3b80d8