[U-Boot] checkpatch.pl checking

Hey all,

As came up in another thread, yes, we do care about what checkpatch.pl says. I've been lax about it as I'd not seen a good way ot integrate it when I looked last. Turns out it's easier to integrate now with the --git arg, so I've got that in my scripts now. Since it would be unfair to reject PRs due to checkpatch.pl issues today, I'm not rejecting, I'm just pointing out the problems it sees. And there will be false positives as sometimes it's fine to go more than 80 chars wide for example (dts files, pinmux stuff). But in general, it shouldn't be complaining, so please take a look. Thanks all!