ide: skip ide_wait_not_busy() on noprobe-disks

There is a problem in some hardware where the kernel will stall for
35 seconds waiting for disks that don't exist. This patch will skip
waiting for the BSY-bit on IDE drives to go away if you set "hdx=noprobe"
as a kernel option and the disk is not marked as 'present' (like when
you set the geometry by hand).

If no noprobe-option is set the code will work (more or less) as the
original but if set the code will skip the ide_wait_not_busy() for
that drive. Even if there would be a drive there and it is still busy
afterwards it should not matter since it isn't probed for later.

The code also honors the MAX_DRIVES variable instead of assuming that
there will be two harddrives on the bus.

Bart: minor cleanups

Signed-off-by: Jonas Stare <jonas.stare@purplescout.se>
CC: Andrew Morton <akpm@linux-foundation.org>,
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>