Use new 'struct disk_op_s' to issue ata requests.

Use new 'struct disk_op_s' to issue ata requests.

Using the struct at all callers reduces the parameter assignments.
Replace ata_op_s with new disk_op_s and update all users.
Unify basic/extended_access methods to use new send_disk_op() func.
Remove cdrom_read_emu -- integrate logic into callers.
Remove ata.h -- move all defs to disk.h