st/omx/tizonia: Add --enable-omx-tizonia flag and build files

Allow only bellagio or tizonia to be used at the same time.
Detect tizonia package config file
Generate libomx_mesa.so and install it to libtizcore.pc::pluginsdir
Only compile empty source (target.c) for now.

GSoC Project link: https://summerofcode.withgoogle.com/projects/#4737166321123328

Acked-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Julien Isorce <julien.isorce@gmail.com>

meson_options.txt

@@ -90,8 +90,8 @@ option(
 option(
   'gallium-omx',
   type : 'combo',
-  value : 'bellagio',
-  choices : ['disabled', 'bellagio'],
+  value : 'tizonia',
+  choices : ['disabled', 'bellagio', 'tizonia'],
   description : 'enable gallium omx state tracker.',
 )
 option(