drm/i915: [sparse] __iomem fixes for debugfs

These were mostly straight forward. No forced casting needed.

Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>
[danvet: fix conflict with ringbuffer_data removal and drop the hunk
about the status page - that needs more care to fix up.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>