Camera: Calculate FOVs for external camera if the information is provided

Currently we set (-1.0, -1.0) as FOV for external cameras.
In this CL, it will try to calculate FOV if the required information is
provided in its metadata.

Bug: 160824680
Test: Run Rotation Vector Test in CTSV on electro.
Change-Id: Ifeb81e4ade9217b854dbf0359ff01df7dac89500