libcamera: v4l2device: Obtain device capabilities

The capabilities structure from the kernel can return capabilities of the
driver, or potentially more specific device capabilities.

Handle this with an inline function 'device_caps()' to return the device
specific capabilities when available, or fall back to the driver capabilities
otherwise.

Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/v4l2_device.cpp

@@ -49,6 +49,13 @@ LOG_DEFINE_CATEGORY(V4L2)
  * \return The string containing the device location
  */
 
+/**
+ * \fn unsigned int V4L2Capability::device_caps()
+ * \brief Retrieve the capabilities of the device
+ * \return The device specific capabilities if V4L2_CAP_DEVICE_CAPS is set or
+ * 	   driver capabilities otherwise
+ */
+
 /**
  * \fn bool V4L2Capability::isCapture()
  * \brief Identify if the device is capable of capturing video