Hello Ethan,
We do not have such document, but basically you need to have the driver from the Vendor Camera, for the Android version + Linux Kernel that you are going to use, Android provide a Sensor API and Sensor Manager to handle the camera, but first need to be added with the Device tree to the Linux Kernel.
You can find details about the Android API from the following link:
Camera | Android Open Source Project
And you Qualcomm has made the following guideline that I consider it is the basic that you need to do for the porting.
