We can't probe all legacy ISA IDE ports by default as the resources may be
occupied by other ISA devices.  Add "probe_mask" module parameter and probe
only first two ISA IDE ports by default leaving the decision about probing
the rest to the user (systems with ISA ide2-6 should be very, very rare).

This fixes a regression caused by:

commit 343a3451
Author: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Date:   Tue Jun 10 20:56:36 2008 +0200

    ide-generic: add missing hwif->chipset setup
...
Reported-by: Mikael Pettersson <mikpe@it.uu.se>
Bisected-by: Mikael Pettersson <mikpe@it.uu.se>
Tested-by: Mikael Pettersson <mikpe@it.uu.se>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>