configure: correctly autodetect xvmc/vdpau/omx

configure: correctly autodetect xvmc/vdpau/omx

Commit e62b7d38a1d (configure: autodetect video state-trackers
when non swrast driver is present) added a check that caused
the autodetection to be omitted when we have the swrast gallium
driver. Whereas it should have skipped the VL targets when only
swrast was selected.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=79907
Cc: "10.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>