i965: Move the pipelined test for SO register access to the screen

i965: Move the pipelined test for SO register access to the screen

Moving the test to the screen places it alongside the other global HW
feature tests that want to be shared between contexts.

Also, we need to know if we support pipelined register writes at
screen creation time so that we can tell if we can expose OpenGL 4.0
in gen7.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>