package/gstreamer1: Allow to build OpenJPEG plugin

The OpenJPEG library is packaged in buildroot (version 1) and there is a
plugin "openjpeg" using it in gst1-plugins-bad. This commit add the option
for building this plugin. It provide a JPEG2000 encoder and decoder.

[Peter: use 'select' instead of 'depends on', sort alphabetically]
Signed-off-by: Vincent Dehors <vincent.dehors@openwide.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>