drm/pci: Deprecate drm_pci_init/exit completely

The magic switching between proper pci driver and shadow-attach isn't
useful anymore since there's no ums+kms drivers left. Let's split this
up properly, calling pci_register_driver for kms drivers and renaming
the shadow-attach init to drm_legacy_pci_init/exit.

Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170524145212.27837-6-daniel.vetter@ffwll.ch