drm: Fix sysfs device confusion.

The drm sysfs class suspend / resume methods could not distinguish
between different device types wich could lead to illegal type casts.

Use struct device_type and make sure the class suspend / resume callbacks
are aware of those. There is no per device-type suspend / resume. Only
new-style PM.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>