frameworks/base: include system/core header camera.h in Camera.h

We define struct CameraInfo in this camera/Camera.h, even though an identical
struct camera_info is defined in hardware/camera.h (but not in
hardware/camera_defs.h).  We may not export struct definitions from the HAL
into headers which may find their way into the NDK.

This commit also renames FRAME_CALLBACK_FLAG_xxx to CAMERA_FRAME_CALLBACK_xxx.

Change-Id: I3e2ddd01d61bf5371ff2fc1a397995e0f1ee11f8
Signed-off-by: Iliyan Malchev <malchev@google.com>