Add initial libcam and example application

Add initial libcam with the following API support:
- cam_init() - Used to initialize a connection with a CAM service
- cam_stream_init() - Used to send the stream initialization message

A simple application is also added which integrates with the libcam
and is capable of communicating with the CAM service.

Signed-off-by: Filipe Rinaldi <filipe.rinaldi@arm.com>
Signed-off-by: Yanqin Wei <yanqin.wei@arm.com>