drm: remove drm_bus->get_name

The only user is the info debugfs file, so we only need something
human readable. Now for both pci and platform devices we've used the
name of the underlying device driver, which matches the name of the
drm driver in all cases. So we can just use that instead.

The exception is usb, which used a generic "USB". Not to harmful with
just one usb driver, but better to use "udl", too.

With that converted we can rip out all the ->get_name implementations.

Reviewed-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>