Vetter: Locking engineering hierarchy

Daniel Vetter continues hisseries on locking in the kernel.

This part goes through a pile of locking pattern and designs, frommost favourable and easiest to adjust and hence resulting in a longterm maintainable code base, to the least favourable since hardestto ensure it works correctly and stays that way while the codeevolves. For convenience even color coded, with the dangerouslevels getting progressively more crispy red indicating how closeto the burning fire you are! Think of it as Dante's Inferno, butfor locking.