ipa: rkisp1: agc: Add a histogram-based gain

As for the IPU3, we can estimate the histogram of the luminance. The
RkISP1 can estimate multiple ones, the R, G and B ones, the Y only one
and a combination of RGB. The one we are interested by in AGC is the Y
histogram.

Use the hardware revision to determine the number of bins of the
produced histogram.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Tested-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/rkisp1/ipa_context.cpp

@@ -71,6 +71,9 @@ namespace libcamera::ipa::rkisp1 {
  * \var IPASessionConfiguration::agc.maxAnalogueGain
  * \brief Maximum analogue gain supported with the configured sensor
  *
+ * \var IPASessionConfiguration::agc.measureWindow
+ * \brief AGC measure window
+ *
  * \var IPASessionConfiguration::hw
  * \brief RkISP1-specific hardware information
  *