ide: add CONFIG_IDE_ARCH_OBSOLETE_DEFAULTS (take 2)

* Add CONFIG_IDE_ARCH_OBSOLETE_DEFAULTS to drivers/ide/Kconfig and use
  it instead of defining IDE_ARCH_OBSOLETE_DEFAULTS in <arch/ide.h>.

v2:
* Define ide_default_irq() in ide-probe.c/ns87415.c if not already defined
  and drop defining ide_default_irq() for CONFIG_IDE_ARCH_OBSOLETE_DEFAULTS=n.

  [ Thanks to Stephen Rothwell and David Miller for noticing the problem. ]

Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>