floppy: prepare ARM code to simplify base address separation

The fd_outb() macro on ARM relies on a special fd_setdor() macro when
the register is FD_DOR and both will need to be changed to accept a
separate base address. Let's just remerge them to simplify the change
and make this code more easily reviewable.

Link: https://lore.kernel.org/r/20200301195555.11154-4-w@1wt.eu
Cc: Ian Molton <spyro@f2s.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>