docs: fix locations of several documents that got moved

The previous patch renamed several files that are cross-referenced
along the Kernel documentation. Adjust the links to point to
the right places.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index 9da6f35..5e9b826 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -921,7 +921,7 @@
 though not all of them are actually meaningful to the kernel.  Boot
 loader authors who need additional command line options for the boot
 loader itself should get them registered in
-Documentation/kernel-parameters.txt to make sure they will not
+Documentation/admin-guide/kernel-parameters.rst to make sure they will not
 conflict with actual kernel options now or in the future.
 
   vga=<mode>