ide-floppy: move /proc handling to ide-floppy_proc.c (take 2)

While at it:
- idefloppy_capacity() -> ide_floppy_capacity()
- idefloppy_proc[] -> ide_floppy_proc[]
- idefloppy_settings[] -> ide_floppy_settings[]

v2:
Build fix for CONFIG_IDE_PROC_FS=n from Elias Oltmanns.

Cc: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>