[ARM] Use helpers for adding pred / CC operands. NFC

Hunt down some of the places where we use bare addReg(0) or addImm(AL).addReg(0)
and replace with add(condCodeOp()) and add(predOps()). This should make it
easier to understand what those operands represent (without having to look at
the definition of the instruction that we're adding to).

Differential Revision: https://reviews.llvm.org/D27984

llvm-svn: 292587