macfb: add vertical blank interrupt

The MacOS driver expects a 60.15Hz vertical blank interrupt to be generated by
the framebuffer which in turn schedules the mouse driver via the Vertical Retrace
Manager.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20211007221253.29024-13-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>