docs: Sphinxify gdb-kernel-debugging.txt and move to dev-tools

Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/dev-tools/tools.rst b/Documentation/dev-tools/tools.rst
index 43f7dee..824ae8e 100644
--- a/Documentation/dev-tools/tools.rst
+++ b/Documentation/dev-tools/tools.rst
@@ -22,3 +22,4 @@
    ubsan
    kmemleak
    kmemcheck
+   gdb-kernel-debugging