lima/gpir: Disallow moves for schedule_first nodes

lima/gpir: Disallow moves for schedule_first nodes

The entire point of schedule_first is that the node has to be scheduled
as soon as possible without any moves because it doesn't produce a
proper floating-point value, or its value changes depending on where you
read it. We were still introducing a move for preexp2 in some cases
though, even if it got scheduled as soon as possible, which broke some
exp() tests. Fix that.

Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Tested-by: Vasily Khoruzhick <anarsoul@gmail.com>