ide: add generic ATA/ATAPI disk driver

* Add struct ide_disk_ops containing protocol specific methods.

* Add 'struct ide_disk_ops *' to ide_drive_t.

* Convert ide-{disk,floppy} drivers to use struct ide_disk_ops.

* Merge ide-{disk,floppy} drivers into generic ide-gd driver.

While at it:
- ide_disk_init_capacity() -> ide_disk_get_capacity()

Acked-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>