Remove nested functions from device iterators.

Remove nested functions from device iterators.

* include/grub/arc/arc.h (grub_arc_iterate_devs_hook_t): New type.
(grub_arc_iterate_devs): Add hook_data argument.
* include/grub/ata.h (grub_ata_dev_iterate_hook_t): New type.
(struct grub_ata_dev.iterate): Add hook_data argument.
* include/grub/device.h (grub_device_iterate_hook_t): New type.
(grub_device_iterate): Add hook_data argument.
* include/grub/disk.h (grub_disk_dev_iterate_hook_t): New type.
(struct grub_disk_dev.iterate): Add hook_data argument.
(grub_disk_dev_iterate): Likewise.
* include/grub/gpt_partition.h (grub_gpt_partition_map_iterate):
Likewise.
* include/grub/msdos_partition.h (grub_partition_msdos_iterate):
Likewise.
* include/grub/partition.h (grub_partition_iterate_hook_t): New
type.
(struct grub_partition_map.iterate): Add hook_data argument.
(grub_partition_iterate): Likewise.
* include/grub/scsi.h (grub_scsi_dev_iterate_hook_t): New type.
(struct grub_scsi_dev.iterate): Add hook_data argument.

Update all callers.