common: migrate the deprecated --mmap/--no-mmap to --load-mode (#26934)

Replace the deprecated --mmap, --no-mmap, --mlock, and --direct-io flags with
the unified --load-mode argument across scripts, examples, and documentation.
Internal warning message and env var docs updated accordingly.

Signed-off-by: Fathi Boudra <fathi.boudra@linaro.org>

scripts/bench-models.sh

@@ -22,8 +22,8 @@ if (( QUICK )); then
 fi
 
 if (( DIO )); then
-    ARGS_BB="${ARGS_BB} --no-mmap --direct-io"
-    ARGS_B="${ARGS_B} -mmp 0 -dio 1"
+    ARGS_BB="${ARGS_BB} --load-mode dio"
+    ARGS_B="${ARGS_B} --load-mode dio"
 fi
 
 run_model() {