ipa: ipu3: Drop sensor controls private members from IPAIPU3

Drop exposure, gain private members from IPAIPU3 because the values
are handled directly via IPAFrameContext.

Move the default vblank value from IPAIPU3 to IPASessionConfiguration
structure as it is a default static value not expected to change
for a session.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/ipu3/ipa_context.cpp

@@ -115,6 +115,9 @@ namespace libcamera::ipa::ipu3 {
  *
  * \var IPASessionConfiguration::sensor.lineDuration
  * \brief Line duration in microseconds
+ *
+ * \var IPASessionConfiguration::sensor.defVBlank
+ * \brief The default vblank value of the sensor
  */
 
 /**