ipa: rpi: agc: Rename "analogue gain" to "gain" where appropriate

Much of the time we use the term "analogue gain" where we really mean
the combined analogue and digital gain (because the digital gain will
make up whatever the analogue gain can't deliver).

This commit replaces the use of "analogue gain" by just "gain" in
places where we really mean the combined gain. There are a couple of
principle areas:

1. Where we previously talked about the "fixedAnalaogueGain"
(including setting it "manually") this is now just the "fixedGain"
(because it always encompassed both analogue and digital gain).

Along with this, the setfixedExposureTime/Gain functions no longer
update the output status directly. Applications should wait in the
usual way for AGC/AEC changes to take effect, and this "shortcut"
actually doesn't fit well with the gain being the combined gain.

2. The divideUpExposure method is adjusted to be clearer that it's
setting the combined gain, and it's prepare() that will discover later
what the analogue gain actually delivered.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/rpi/common/ipa_base.cpp

@@ -868,7 +868,7 @@ void IpaBase::applyControls(const ControlList &controls)
 			if (agc->autoGainEnabled())
 				break;
 
-			agc->setFixedAnalogueGain(0, ctrl.second.get<float>());
+			agc->setFixedGain(0, ctrl.second.get<float>());
 
 			libcameraMetadata_.set(controls::AnalogueGain,
 					       ctrl.second.get<float>());