i965: Only emit VF cache invalidations when the high bits changes

i965: Only emit VF cache invalidations when the high bits changes

Commit 92f01fc5f914 ("i965: Emit VF cache invalidates for 48-bit
addressing bugs with softpin.") tried to only emit the VF invalidate if
the high bits changed, but it accidentally always set need_invalidate to
true; causing it to emit unconditionally emit the pipe control before
every primitive.

Fixes: 92f01fc5f914 ("i965: Emit VF cache invalidates for 48-bit addressing bugs with softpin.")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106708
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>