drm: Move vblank related module options into drm_irq.c

This allows us to drop 2 header declarations from drmP.h. The 3rd one
is also used in drm_ioctl.c, so for that create a new drm_internal.h
header for non-legacy non-kms (since we have internal headers for
those parts already) declarations private to drm.ko.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>