mesa: Expose RESET_NOTIFICATION_STRATEGY with KHR_robustness.

mesa: Expose RESET_NOTIFICATION_STRATEGY with KHR_robustness.

This is supposed to be exposed with the GL_KHR_robustness extension,
which we support on ES 2.0 and later.  On desktop GL, it's also exposed
by GL_ARB_robustness, which is supported by all drivers ("dummy_true").
so we also allow desktop GL.

Fixes:
- ES32-CTS.robust.robustness.noResetNotification
- ES32-CTS.robust.robustness.loseContextOnReset

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>