Documentation: add pointer to name_to_dev_t for root= values

Update kernel-parameters.txt to point users to the authoritative comment
for name_to_dev_t. In addition, updates other places where some
name_to_dev_t behavior was discussed. All other references to root=
appear to be for explicit sample usage or just side comments when
discussing other kernel parameters.

Signed-off-by: Will Drewry <[e-mail]>
Cc: Kay Sievers <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Trond Myklebust <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/frv/booting.txt

···
       To use the first on-chip serial port at baud rate 115200, no parity, 8
       bits, and no flow control.
 
-  (*) root=/dev/<xxxx>
+  (*) root=<xxxx>
 
-      This specifies the device upon which the root filesystem resides. For
-      example:
+      This specifies the device upon which the root filesystem resides. It
+      may be specified by major and minor number, device path, or even
+      partition uuid, if supported.  For example:
 
 	/dev/nfs	NFS root filesystem
 	/dev/mtdblock3	Fourth RedBoot partition on the System Flash
+	PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF/PARTNROFF=1
+		first partition after the partition with the given UUID
+	253:0		Device with major 253 and minor 0
+
+      Authoritative information can be found in
+      "Documentation/kernel-parameters.txt".
 
   (*) rw
 

Documentation/kernel-parameters.txt

···
 	ro		[KNL] Mount root device read-only on boot
 
 	root=		[KNL] Root filesystem
+			See name_to_dev_t comment in init/do_mounts.c.
 
 	rootdelay=	[KNL] Delay (in seconds) to pause before attempting to
 			mount the root filesystem

Documentation/m68k/kernel-options.txt

···
 the first of these. You can find out all valid major numbers by
 looking into include/linux/major.h.
 
+In addition to major and minor numbers, if the device containing your
+root partition uses a partition table format with unique partition
+identifiers, then you may use them.  For instance,
+"root=PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF".  It is also
+possible to reference another partition on the same device using a
+known partition UUID as the starting point.  For example,
+if partition 5 of the device has the UUID of
+00112233-4455-6677-8899-AABBCCDDEEFF then partition 3 may be found as
+follows:
+  PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF/PARTNROFF=-2
+
+Authoritative information can be found in
+"Documentation/kernel-parameters.txt".
+
 
 2.2) ro, rw
 -----------