[arm] make rf flags virtualizable again
[arm] make rf flags virtualizable again

Makes more sense now after getting rid of branchy flag computation. Might
give slight slowdown (~5%) than w/o virtualizables, but seems more
reliable. W/o virtualizables (prev commit) crashed on a benchmark.

cornell-brg/pydgin,futurecore/pydgin,moreati/pydgin,cornell-brg/pydgin,moreati/pydgin,futurecore/pydgin,futurecore/pydgin,cornell-brg/pydgin,moreati/pydgin,cornell-brg/pydgin,futurecore/pydgin,moreati/pydgin