drm/doc: include xe_drm.h

Make sure the uapi gets picked up by the normal docs build.

Signed-off-by: Matthew Auld <[e-mail]>
Cc: Francois Dugast <[e-mail]>
Cc: Lucas De Marchi <[e-mail]>
Reviewed-by: Francois Dugast <[e-mail]>
Signed-off-by: Rodrigo Vivi <[e-mail]>

Documentation/gpu/driver-uapi.rst

···
     :doc: Overview
 
 .. kernel-doc:: include/uapi/drm/nouveau_drm.h
+
+drm/xe uAPI
+===========
+
+.. kernel-doc:: include/uapi/drm/xe_drm.h