Add definition of SM and arm for MCS FITS files

MCS image covers all four spectrographs (or all 2396 science fibers) in one image, there will no number for spectrograph module nor armNum.
As for now, we assume to save the last shot for confirmation of the fiber positions on exposure from MCS to archive, but nothing others (will save into ICS storage, but not push to archive, which might be discussed later).

So, propose to set
PF%sC%6d00.fits
for MCS FITS file name.