configure: add option --enable-native-buffer default is on

only if __NATIVE_BUFFER_DEFAULT__ is set to 1, ProcessorEnableNativeBuffers
is called when the port is disabled.

gst-omx do not know the details of VideoRenderBuffer

Signed-off-by: Xu Guangxin <guangxin.xu@intel.com>
Signed-off-by: Zhao Halley <halley.zhao@intel.com>
configure: add config option --use-libvacodec

preload libvacodec libs when --enable-libvacodec is used