Camera: Set focal length for external camera if the information is provided

Currently, we will set -1.0 as the default focal length for external
camera even if camera HAL provides the information. We should respect
the information if it is provided.

Bug: 141517606
Test: cts-tradefed run commandAndExit cts -m CtsCameraTestCases -t
android.hardware.cts.CameraTest#testJpegExif

Change-Id: Iae38ed0243a386187e29c5c4549d92ca24f58d0d