video: da8xx-fb: enable sync lost intr for v2 ip

The interrupt handler explicitly has code that handles the sync lost
interrupt.  However the sync lost interrupt is never actually being
enabled in the LCD controller, therefore this interrupt code path is not
being exercised.  This fix simply enables the generation of the sync
lost interrupt by the LCD controller so it can be dealt with
appropriately by the interrupt handler.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>