[arm] more register labels/documentation
[arm] more register labels/documentation

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