Doc: Improve docs for file permission checking on NTFS

- Reduce verbosity in qfiledevice.cpp
- Copy to qfileinfo.cpp

Task-number: QTBUG-35232
Change-Id: I4b0de36bdf266ebf486f73daecec8fbb74fa1d4c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>