drm: Move struct drm_device.pdev to legacy section

Struct drm_device.pdev is being moved to legacy status as only legacy
DRM drivers use it. A possible follow-up patchset could remove pdev
entirely.

v4:
	* rebased

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210429105101.25667-6-tzimmermann@suse.de