Add DragonFly's partition number to fdisk(8) and diskmbr.h

This change doesn't make any attempt to add support for these slices to the
relevent GEOM classes.  Just register the number in fdisk and the canonical
list of kernel macros (diskmbr.h).

Obtained from:	DragonFlyBSD (794d80aa519b394b3174f20776a) (small subset of)

sbin/fdisk/fdisk.c

@@ -175,6 +175,7 @@ static const char *const part_types[256] = {
 	[0x63] = "System V/386 (such as ISC UNIX), GNU HURD or Mach",
 	[0x64] = "Novell Netware/286 2.xx",
 	[0x65] = "Novell Netware/386 3.xx",
+	[0x6C] = "DragonFlyBSD",
 	[0x70] = "DiskSecure Multi-Boot",
 	[0x75] = "PCIX",
 	[0x77] = "QNX4.x",

sys/sys/disk/mbr.h

@@ -50,6 +50,7 @@
 #define	DOSPTYP_EXTLBA	0x0f	/* DOS extended partition */
 #define	DOSPTYP_PPCBOOT	0x41	/* PReP/CHRP boot partition */
 #define	DOSPTYP_LDM	0x42	/* Win2k dynamic extended partition */
+#define	DOSPTYP_DFLYBSD	0x6c	/* DragonFlyBSD partition type */
 #define	DOSPTYP_LINSWP	0x82	/* Linux swap partition */
 #define	DOSPTYP_LINUX	0x83	/* Linux partition */
 #define	DOSPTYP_LINLVM	0x8e	/* Linux LVM partition */