log: global: Rename warn_non_spl()

This should now refer to xPL rather than SPL, so update it throughout
the tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/logging.rst b/doc/develop/logging.rst
index 704a6bf..d7a40c9 100644
--- a/doc/develop/logging.rst
+++ b/doc/develop/logging.rst
@@ -292,7 +292,7 @@
 
 Convert error() statements in the code to log() statements
 
-Figure out what to do with BUG(), BUG_ON() and warn_non_spl()
+Figure out what to do with BUG(), BUG_ON() and warn_non_xpl()
 
 Add a way to browse log records