- clear hwif->hw in setup-pci.c before using it

- fix arch/arm/Kconfig to allow IDE only on platforms supporting it

- introduce IDE_ARCH_OBSOLETE_INIT and ide_default_io_ctl() so
  we can use generic ide_init_hwif_ports() and kill no longer needed
  <asm-arm/arch-*/ide.h> (leave broken lh7a40x and sa1100 versions)

Cross-compile tested on ARM.