disk: dos: add some defines for the hardcoded numbers

Add some handy defines for some hardcoded magic numbers related to
extended partition handling.
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>

disk/part_dos.c

@@ -42,9 +42,9 @@ static inline unsigned int le32_to_int(unsigned char *le32)
 
 static inline int is_extended(int part_type)
 {
-    return (part_type == 0x5 ||
-	    part_type == 0xf ||
-	    part_type == 0x85);
+    return (part_type == DOS_PART_TYPE_EXTENDED ||
+	    part_type == DOS_PART_TYPE_EXTENDED_LBA ||
+	    part_type == DOS_PART_TYPE_EXTENDED_LINUX);
 }
 
 static int get_bootable(dos_partition_t *p)

disk/part_dos.h

@@ -15,6 +15,9 @@
 #define DOS_PBR_MEDIA_TYPE_OFFSET	0x15
 #define DOS_MBR	0
 #define DOS_PBR	1
+#define DOS_PART_TYPE_EXTENDED		0x05
+#define DOS_PART_TYPE_EXTENDED_LBA	0x0F
+#define DOS_PART_TYPE_EXTENDED_LINUX	0x85
 
 typedef struct dos_partition {
 	unsigned char boot_ind;		/* 0x80 - active			*/