doc: drivers: add a paragraph mentioning the initlevels target

Add a paragraph mentioning the initlevels target for inspecting the
DEVICE_DEFINE and SYS_INIT sequence.

(cherry picked from commit bc43e89)

Original-Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
GitOrigin-RevId: bc43e89
Change-Id: I706024cecb8dd47f2c42706e0b31f964d17b63e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/4987906
Tested-by: Fabio Baltieri <fabiobaltieri@google.com>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Reviewed-by: Fabio Baltieri <fabiobaltieri@google.com>
Commit-Queue: Fabio Baltieri <fabiobaltieri@google.com>

doc/kernel/drivers/index.rst

@@ -394,6 +394,18 @@ In some cases you may just need to run a function at boot. For such cases, the
 data structures and there isn't a way to later get a device pointer by name. The
 same device policies for initialization level and priority apply.
 
+Inspecting the initialization sequence
+**************************************
+
+Device drivers declared with :c:macro:`DEVICE_DEFINE` (or any variations of it)
+and :c:macro:`SYS_INIT` are processed at boot time and the corresponding
+initialization functions are called sequentially according to their specified
+level and priority.
+
+Sometimes it's useful to inspect the final sequence of initialization function
+call as produced by the linker. To do that, use the ``initlevels`` CMake
+target, for example ``west build -t initlevels``.
+
 Error handling
 **************