[SETUPLIB] Detect GPT-partitioned disks but don't use them since we don't support them at the moment.

- Add checks for GPT disks and either fail or ignore the disk,
  depending on the operation being executed.

[USETUP][REACTOS] Display the disk style more accurately.

base/setup/lib/utils/partlist.h

@@ -118,7 +118,7 @@ typedef struct _DISKENTRY
     BOOLEAN Dirty;
 
     BOOLEAN NewDisk; /* If TRUE, the disk is uninitialized */
-    BOOLEAN NoMbr;   /* If TRUE, the MBR is absent */  // See r40437
+    PARTITION_STYLE DiskStyle;  /* MBR/GPT-partitioned disk, or uninitialized disk (RAW) */
 
     UNICODE_STRING DriverName;
 
@@ -174,6 +174,11 @@ typedef struct _PARTLIST
 
 #define  PARTITION_TBL_SIZE 4
 
+#define PARTITION_MAGIC     0xAA55
+
+/* Defines system type for MBR showing that a GPT is following */
+#define EFI_PMBR_OSTYPE_EFI 0xEE
+
 #include <pshpack1.h>
 
 typedef struct _PARTITION