Move function dependent resetting of a subtarget variable out of the

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.

llvm-svn: 212309