Input: add to kernel-api docbook

Add input subsystem to kernel-api docbook.
Enhance some function and parameter comments.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/drivers/input/ff-memless.c b/drivers/input/ff-memless.c
index cd8b729..eba18b6 100644
--- a/drivers/input/ff-memless.c
+++ b/drivers/input/ff-memless.c
@@ -460,7 +460,7 @@
 }
 
 /**
- * input_ff_create_memless() - create memoryless FF device
+ * input_ff_create_memless() - create memoryless force-feedback device
  * @dev: input device supporting force-feedback
  * @data: driver-specific data to be passed into @play_effect
  * @play_effect: driver-specific method for playing FF effect