ata: Security fixes, improved API, refactoring

- Change public API to be simpler, and similar to NVMe
- Remove secondary drives from API, they aren't going to be supported
- Fix ATA_REG_DATA buffer size checking resulting in heap corruptions under LLVM Fuzzer
- Put the device under lock, LLVM Fuzzer reliably abused it by resetting & operating ATA at the same time
- Limit PRDT size to 65536 to prevent malicious guests from hanging the IO thread in an infinite loop
- Fix misaligned reads in ata_process_prdt() found by UBSAN
- General refactoring, fix PVS warnings