drm/xe: Wire up devcoredump in documentation

Add a documentation page to detail the device coredump as implemented by
xe - it was documented in the source code, but not visible in the
rendered (html) documentation.

Reviewed-by: Matthew Brost <[e-mail]>
Reviewed-by: Raag Jadav <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>

Documentation/gpu/xe/index.rst

···
    xe_firmware
    xe_tile
    xe_debugging
+   xe_devcoredump
    xe-drm-usage-stats.rst

Documentation/gpu/xe/xe_devcoredump.rst

···
+.. SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+
+==================
+Xe Device Coredump
+==================
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_devcoredump.c
+   :doc: Xe device coredump
+
+Internal API
+============
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_devcoredump.c
+   :internal: