Wip/matt auld/dynamic oa configs v2

[matt-auld]

Feel free to take a look when you get the time. Thanks.

As per your comments:

• We now silently fail when given an empty OA register set
• We now check that at least one register set is given, be it MUX, BOOL or FLEX
• We now explicitly check the uuid format from user-space - this is still just treated as a string and not a 128bit value
  • I did look into using the 128bit form for the uuid, but I couldn't find any helpful kernel utilities, other than this https://lwn.net/Articles/356868/. Something like uuid_unparse would be really nice here.
• We now check for a uuid collision early on
• We now return from the icotl the metric-set id, rather than storing it in the user struct - much cleaner

Also note the "remove redundant metric set check" commit, am I correct in making this change, to me both checks seem to do the same thing. If so feel free to squash with your commits, otherwise just disregard.

I think some kind of locking is still needed.

[matt-auld]

Ah right, cool, yeah I opted for the former given that the unconditional check ensures the metric_set has a sensible value before continuing(as in if no metric set is given). I must have missed _init_stream_code, is this in your branch, or am I just blind? I'll rebase this when you push those changes.