docs: debugging-via-ohci1394.txt: add it to the core-api book

There is an special chapter inside the core-api book about
some debug infrastructure like tracepoints and debug objects.

It sounded to me that this is the best place to add a chapter
explaining how to use a FireWire controller to do remote
kernel debugging, as explained on this document.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/9b489d36d08ad89d3ad5aefef1f52a0715b29716.1588345503.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/kernel-parameters.txt

@@ -3329,7 +3329,7 @@
 			See Documentation/admin-guide/sysctl/vm.rst for details.
 
 	ohci1394_dma=early	[HW] enable debugging via the ohci1394 driver.
-			See Documentation/debugging-via-ohci1394.txt for more
+			See Documentation/core-api/debugging-via-ohci1394.rst for more
 			info.
 
 	olpc_ec_timeout= [OLPC] ms delay when issuing EC commands

Documentation/core-api/index.rst

@@ -98,6 +98,7 @@ Interfaces for kernel debugging
 
    debug-objects
    tracepoint
+   debugging-via-ohci1394
 
 Everything else
 ===============

lib/Kconfig.debug

@@ -1508,7 +1508,7 @@ config PROVIDE_OHCI1394_DMA_INIT
 	  This code (~1k) is freed after boot. By then, the firewire stack
 	  in charge of the OHCI-1394 controllers should be used instead.
 
-	  See Documentation/debugging-via-ohci1394.txt for more information.
+	  See Documentation/core-api/debugging-via-ohci1394.rst for more information.
 
 source "samples/Kconfig"