drm/panic: Move drm_panic_register prototype to drm_crtc_internal.h

drm/panic: Move drm_panic_register prototype to drm_crtc_internal.h

drm_panic_[un]register() are only used by the core drm, and are not
intended to be called by other drm drivers, so move their prototypes
to drm_crtc_internal.h.

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240807134902.458669-4-jfalempe@redhat.com