mime/cupsfilters-ghostscript.convs: Add conversion rule for PCLm output
As Ghostscript is capable of producing PCLm output, add a conversion
rule to convert PDF into PCLm with gstoraster.
application/postscript application/pdf 0 gstopdf
application/vnd.cups-pdf application/vnd.cups-raster 99 gstoraster
application/vnd.cups-pdf image/pwg-raster 99 gstoraster
+application/vnd.cups-pdf application/PCLm 99 gstoraster
application/vnd.cups-postscript application/vnd.cups-raster 175 gstoraster
