camera: Fix various focus-related errors

* Validate that the focus region is within legal boundaries
* Reset the region to sane values if bad ones are given
* Set a default empty region
* If auto focus exists, it must be the default

Fixes android.hardware.cts.CameraTest#testFocusAreas and
android.hardware.cts.CameraTest#testParameters

Change-Id: I3aafcccc2c6081ba44edb3283a850c55178fa90a