ipa: ipu3: Initialize CameraSensorHelper at IPU3 init stage

In order for the CameraSensorHelper to be instantiated, we need to find
its factory using the camera sensor model name stored in
IPASettings::sensorModel. As we don't need to do it at each configure
call (the sensor is not changing in-between), implement the init call in
IPAIPU3 to do that.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>