drm: rcar-du: Split CRTC IRQ and Clock features

Not all platforms require both per-crtc IRQ and per-crtc clock
management. In preparation for suppporting such platforms, split the
feature macro to be able to specify both features independently.

The other features are incremented accordingly, to keep the two crtc
features adjacent.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>