atad: disable DVRP workaround for LBA48-aware DVRP firmware

[pcm720]

The current workaround implementation forces LBA28 if it detects a DVRP-emulated hard drive.
This PR adds support for LBA48-aware DVRP firmware by checking for the "PS2LBA48" magic signature added by a compatible CFW in ATA IDENTIFY words 121-124.

This allows full LBA48 for PSX consoles with custom firmware while keeping backwards compatibility with the original firmware.
Tested on PSX DESR-7100 with DVRPwned 2.0.0:

  atad: LBA48-capable DVRP firmware detected, disabling the workaround
  hdd: disk0: 0x161e70f6 sectors, max 0x00800000
  hdd: drive status 0, format version 00000002
  hdd: version 0205 driver start. This is OSD version!

  Testing LBA48 support:
        Testing sectors 0x20000-0x10020000
        memcmp results: 0x00 0xde 0xde 0x00 0x00 0xde
  
  LBA48 test OK
        Testing sectors 0x2000000-0x12000000
        memcmp results: 0xffffff89 0x67 0x67 0x00 0x00 0xde
  
  LBA48 test OK

[uyjulian]

Lgtm