Provide face and orientation info from gstreamer camera backend.

Cleans up duplicate device enumeration code so the devices listed by
the QMediaServiceProviderPlugin are the same as those in the
QVideoInputDeviceControl and includes face and orientation information
if available.

Change-Id: Iaa4c303c973bcf3e0f7c8c2fd7a7de629bccec86
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>