dri: Use designated initializers for DRI extension structs

dri: Use designated initializers for DRI extension structs

The dri directory is compiled with -std=c99. There is no excuse to not use
designated initializers.

As a nice benefit, the code is now more friendly to grep. Without
designated initializers, psychic prowess is required to find the
initialization of DRI extension function pointers with grep.  I have
observed several people, when they first encounter the DRI code, fail at
statically chasing the DRI function pointers due to this problem.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>