[Intel-gfx] enabling forcewake from userspace

[Ben Widawsky]

Chris, do you already have something like this queued up?

I don't have a SNB with which to test this patch right now. I'd like to
know if anyone has any major issues with this, because I intend to use
this to enable userspace to properly read and write registers on SNB.

Also if you see any glaring issues before I get to testing it, might as
well point them out now :p

Ben