Enable CL image processor via xcamsrc plugin

Image processor and 3A analyzer can be configured via set_property.
Restructure MainDeviceManager to reuse more from DeviceManager.
gstxcamsrc can handle both drm bo buffer and v4l2 buffer now.
diff --git a/xcore/buffer_pool.cpp b/xcore/buffer_pool.cpp
index 1e36c6d..a761af4 100644
--- a/xcore/buffer_pool.cpp
+++ b/xcore/buffer_pool.cpp
@@ -59,6 +59,13 @@
     return _data->unmap ();
 }
 
+int
+BufferProxy::get_fd ()
+{
+    XCAM_ASSERT (_data.ptr ());
+    return _data->get_fd ();
+}
+
 BufferPool::BufferPool ()
     : _allocated_num (0)
     , _max_count (0)