ide: merge ide_arm and ide_generic host drivers

There is no need for a separate ide_arm host driver nowadays
so merge it into ide_generic one.

While at it:
- return -EBUSY from ide_generic_init() if I/O resources are busy
- scale down ide_generic_check_pci_legacy_iobases() for CONFIG_PCI=n

Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Alexander Schulz <alex@shark-linux.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>