The code has become quite hairy. By relocating all the generic registers
it will become more obvious where future ones should go. There is still
admittedly a bit of confusion left for things like per ring registers.

A subsequent patch will clean this function up.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>