Camera: Maintain set of non-external cameras

External cameras are currently identified by comparison of camera ID
and stored number of legacy cameras reported by camera HAL. This simple
check assumes that a legacy camera ID belong to range <0,
mNumberOfLegacyCameras>.

Some camera HALs support camera ID remapping so its legacy camera IDs
can be arbitrary number also outside the specified range.

Maintain the set of non-external (legacy) cameras and use this set to
check if particular camera is legacy or external one at existing places.

Change-Id: I78670a39b2c6f650d49d666c521335b7167a594a