dri: Optionally turn off a couple of GLX extensions based on driconf options

dri: Optionally turn off a couple of GLX extensions based on driconf options

With GLX_EXT_buffer_age turned on, gnome-shell will use full-screen damage
with GLX, which severely hurts performance with architectures that emulate
page-flips with copies. Like vmware. We would like to be able to turn off that
extension. Similarly, typically the GLX_OML_sync_control doesn't make much
sense on a virtual architecture since we don't really sync to the host's
vertical retrace. We'd like to be able to turn it off as well.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>