[arm] implement umlal, fix decoder ambiguity
[arm] implement umlal, fix decoder ambiguity

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