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>

drivers/input/ff-core.c

@@ -203,7 +203,7 @@ static int erase_effect(struct input_dev *dev, int effect_id,
 }
 
 /**
- * input_ff_erase - erase an effect from device
+ * input_ff_erase - erase a force-feedback effect from device
  * @dev: input device to erase effect from
  * @effect_id: id of the ffect to be erased
  * @file: purported owner of the request
@@ -347,7 +347,7 @@ EXPORT_SYMBOL_GPL(input_ff_create);
 
 /**
  * input_ff_free() - frees force feedback portion of input device
- * @dev: input device supporintg force feedback
+ * @dev: input device supporting force feedback
  *
  * This function is only needed in error path as input core will
  * automatically free force feedback structures when device is