Camera: Add bandaid for preview orientation on reverse-landscape cameras

Camera sensors on Android may be either landscape or reverse-landscape
oriented, but the vast majority of shipping devices only use landscape.

This means that many camera-using apps (which are generally forcing
themselves to landscape orientation) never call setDisplayOrientation,
since its default value of 0 is correct for the majority of devices.

However, there are some reverse-landscape devices, and for those, such
apps get upside-down preview.

This bandaid changes the default value of displayOrientation to be 180
on such devices, so that apps that never call setDisplayOrientation get
correct preview.  This bandaid has no effect on apps that do call
setDisplayOrientation, so hopefully such apps are doing the math
correctly.

Also update documentation to indicate that setDisplayOrientation should
be called, and to note the change in default orientation behavior in
Android N.

Change-Id: I1b2c957642fda8edead61bd07eda9d18c38d1fe6
Fixes: 27840948