docs: blockdev: add it to the admin-guide

The blockdev book basically contains user-faced documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/admin-guide/blockdev/drbd/node-states-8.dot

@@ -11,4 +11,3 @@ digraph peer_states {
 	Unknown   -> Primary           [ label = "connected" ]
 	Unknown   -> Secondary         [ label = "connected" ]
 }
-

Documentation/admin-guide/blockdev/index.rst

@@ -1,5 +1,3 @@
-:orphan:
-
 ===========================
 The Linux RapidIO Subsystem
 ===========================

Documentation/admin-guide/index.rst

@@ -73,6 +73,7 @@ configure specific aspects of kernel behavior to your liking.
    java
    ras
    bcache
+   blockdev/index
    ext4
    binderfs
    pm/index

Documentation/admin-guide/kernel-parameters.txt

@@ -1249,7 +1249,7 @@
 			See also Documentation/fault-injection/.
 
 	floppy=		[HW]
-			See Documentation/blockdev/floppy.rst.
+			See Documentation/admin-guide/blockdev/floppy.rst.
 
 	force_pal_cache_flush
 			[IA-64] Avoid check_sal_cache_flush which may hang on
@@ -2234,7 +2234,7 @@
 	memblock=debug	[KNL] Enable memblock debug messages.
 
 	load_ramdisk=	[RAM] List of ramdisks to load from floppy
-			See Documentation/blockdev/ramdisk.rst.
+			See Documentation/admin-guide/blockdev/ramdisk.rst.
 
 	lockd.nlm_grace_period=P  [NFS] Assign grace period.
 			Format: <integer>
@@ -3268,7 +3268,7 @@
 
 	pcd.		[PARIDE]
 			See header of drivers/block/paride/pcd.c.
-			See also Documentation/blockdev/paride.rst.
+			See also Documentation/admin-guide/blockdev/paride.rst.
 
 	pci=option[,option...]	[PCI] various PCI subsystem options.
 
@@ -3512,7 +3512,7 @@
 			needed on a platform with proper driver support.
 
 	pd.		[PARIDE]
-			See Documentation/blockdev/paride.rst.
+			See Documentation/admin-guide/blockdev/paride.rst.
 
 	pdcchassis=	[PARISC,HW] Disable/Enable PDC Chassis Status codes at
 			boot time.
@@ -3527,10 +3527,10 @@
 			and performance comparison.
 
 	pf.		[PARIDE]
-			See Documentation/blockdev/paride.rst.
+			See Documentation/admin-guide/blockdev/paride.rst.
 
 	pg.		[PARIDE]
-			See Documentation/blockdev/paride.rst.
+			See Documentation/admin-guide/blockdev/paride.rst.
 
 	pirq=		[SMP,APIC] Manual mp-table setup
 			See Documentation/x86/i386/IO-APIC.rst.
@@ -3642,7 +3642,7 @@
 
 	prompt_ramdisk=	[RAM] List of RAM disks to prompt for floppy disk
 			before loading.
-			See Documentation/blockdev/ramdisk.rst.
+			See Documentation/admin-guide/blockdev/ramdisk.rst.
 
 	psi=		[KNL] Enable or disable pressure stall information
 			tracking.
@@ -3664,7 +3664,7 @@
 	pstore.backend=	Specify the name of the pstore backend to use
 
 	pt.		[PARIDE]
-			See Documentation/blockdev/paride.rst.
+			See Documentation/admin-guide/blockdev/paride.rst.
 
 	pti=		[X86_64] Control Page Table Isolation of user and
 			kernel address spaces.  Disabling this feature
@@ -3693,7 +3693,7 @@
 			See Documentation/admin-guide/md.rst.
 
 	ramdisk_size=	[RAM] Sizes of RAM disks in kilobytes
-			See Documentation/blockdev/ramdisk.rst.
+			See Documentation/admin-guide/blockdev/ramdisk.rst.
 
 	random.trust_cpu={on,off}
 			[KNL] Enable or disable trusting the use of the