ide-floppy: add a debug_mask module parameter

... with which to control to verbosity of debug messages on module load time.

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
[bart: no need to zero debug_mask + move module_param() closer debug_mask]
[bart: init drive->debug_mask in ide_floppy_probe() not in idefloppy_open()]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>