main: Add driver cache blob fields to gl_program

These fields can be used to optionally save off a driver blob with the
program metadata. For example, serialized nir, or tgsi.

v3:
 * Rename serialized_nir* to driver_cache_blob*. (Tim)
 * Free memory. (Jason)

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/mesa/program/program.c

@@ -279,6 +279,10 @@ _mesa_delete_program(struct gl_context *ctx, struct gl_program *prog)
       ralloc_free(prog->sh.BindlessImages);
    }
 
+   if (prog->driver_cache_blob) {
+      ralloc_free(prog->driver_cache_blob);
+   }
+
    ralloc_free(prog);
 }