ipa: raspberrypi: alsc: Limit the calculated lambda values

Under the right circumstances, the alsc calculations could spread the colour
errors across the entire image as lambda remains unbound. This would cause the
corrected image chroma values to slowly drift to incorrect values.

This change adds a config parameter (alsc.lambda_bound) that provides an upper
and lower bound to the lambda value at every stage of the calculation. With this
change, we now adjust the lambda values so that the average across the entire
grid is 1 instead of normalising to the minimum value.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

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