Useless bootargs

Hi, while going over the bootargs we pass to iMX6 (inherited from those we pass to iMX53, in turn inherited from those we pass to Panda, probably at some point inherited from what we used to pass to Beagle, .....), I spotted a few boot arguments I didn't know the meaning of - so I grep -r-ed the codebase to see what they do.

In some cases, it turns out they do nothing at all because there's nothing at all checking for them in current environments at least on iMX* ("nocompcache", "fixrtc").

Probably every board maintainer should go over his boot args and remove the useless ones at some point.

ttyl bero