Move function dependent resetting of a subtarget variable out of the
subtarget. This involved having the movt predicate take the current
function - since we care about size in instruction selection for
whether or not to use movw/movt take the function so we can check
the attributes. This required adding the current MachineFunction to
FastISel and propagating through.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212309 91177308-0d34-0410-b5e6-96231b3b80d8