Go through all kinds of trouble to mark 'blr' as having a predicate operand

Go through all kinds of trouble to mark 'blr' as having a predicate operand
that takes a register and condition code.  Print these pieces of BLR the
right way, even though it is currently set to 'always'.

Next up: get the JIT encoding right, then enhance branch folding to produce
predicated blr for simple examples.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31449 91177308-0d34-0410-b5e6-96231b3b80d8