menu: new fast step rate feature

Signed-off-by: Janar Sööt <janar.soot@gmail.com>

config/example-menu.cfg

@@ -116,6 +116,11 @@
 #   This is mandatory attribute for input.
 #   It accepts positive integer or float value. Will determine increment
 #   and decrement steps for edit value.
+#input_step2:
+#   This is optional attribute for input.
+#   It accepts positive integer or float value. Will determine fast rate
+#   increment and decrement steps for edit value.
+#   The default is 0 (input_step will be used instead)
 
 #[menu list1]
 #type:list or vsdcard