[FREELDR] Simplify code by using a AddReactOSArcDiskInfo() helper, and few extra additions.
- Introduce the AddReactOSArcDiskInfo() helper to get rid of the
duplicated reactos_arc_disk_info usage scattered amongst different
files.
- GetHarddiskInformation(): If we cannot read the disk that has been
enumerated by the BIOS, return a default identifier string.
- GetHarddiskInformation(): The last character of the disk identifier
string corresponds to whether its MBR is "valid"/has the 0xAA55
signature (use 'A') or whether it's not (use 'X'). Tested on Windows.
- Split PcInitializeBootDevices() in two: the first part of this
function that enumerates hard disks from the BIOS is now moved into
EnumerateHarddisks().
- The 'ValidPartitionTable' field of the ARC disk signature records must
be initialized with correct value that is specified in the different
AddReactOSArcDiskInfo() calls.