libcamera: Document documentation style and update the code accordingly

The documentation style for the Doxygen comment blocks is inconsistent
in the library. Document the expectations and update all existing
comment blocks to match.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/stream.cpp

@@ -88,14 +88,12 @@ namespace libcamera {
 /**
  * \fn StreamUsage::role()
  * \brief Retrieve the stream role
- *
  * \return The stream role
  */
 
 /**
  * \fn StreamUsage::size()
  * \brief Retrieve desired size
- *
  * \return The desired size
  */