swrast: add dri2ConfigQueryExtension to the correct extension list

swrast: add dri2ConfigQueryExtension to the correct extension list

The extension should be in the list as returned by getExtensions().
Seems to have gone unnoticed since close to nobody wants to change the
vblank mode for the software driver.

v2: Rebase

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com> (v1)
(cherry picked from commit 7791949dadd5af707055d0076874177e5e8e2133)
[Emil Velikov: drop st/dri hunk, squash correct swrast piece]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>