libs/utils/trace: factor out trace class invocation
libs/utils/trace: factor out trace class invocation

trappy.SysTrace() and trappy.FTrace() accept the same arguments (and we
want that to continue to be).  Factor out the invocation of the class
below the condition to avoid repeating the arguments.

joelagnel/lisa,credp/lisa,credp/lisa,mdigiorgio/lisa,credp/lisa,bjackman/lisa,joelagnel/lisa,JaviMerino/lisa,bjackman/lisa,credp/lisa,ARM-software/lisa,ARM-software/lisa,ARM-software/lisa,arnoldlu/lisa,mdigiorgio/lisa,arnoldlu/lisa,ARM-software/lisa