i965/gen6/gs: Handle case where a GS doesn't allocate VUE

We can not use the VUE Dereference flags combination for EOT
message under ILK and SNB because the threads are not initialized
there with initial VUE handle unlike Pre-IL.
So to avoid GPU hangs on SNB and ILK we need
to avoid usage of the VUE Dereference flags combination.
(Was tested only on SNB but according to the specification
SNB Volume 2 Part 1: 1.6.5.3, 1.6.5.6
the ILK must behave itself in the similar way)

v2: Approach to fix this issue was changed.
Instead of different EOT flags in the program end
we will create VUE every time even if GS produces no output.

v3: Clean up the patch.
Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105399


CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>
(cherry picked from commit 232c5d75)