run target AMIP runs on GPU

[juliasloan25]

Following #572, we have a simple AMIP run working on GPU. The next step is to add in GPU runs for the target simulations we're actually interested in. As we add these longruns, we can first test for a shorter simulation time to make sure they run, then add GPU longruns once we're confident they'll work.

part of #390
closed by #632