OMAP3+: SR: disable interrupt by default

We will enable and disable interrupt on a need basis in the class
driver. We need to keep the IRQ disabled by default else the
forceupdate or vcbypass events could trigger events that we don't
need/expect to handle.

This is a preparation for SmartReflex AVS class drivers such as
class 2 and class 1.5 which would need to use interrupts. Existing
SmartReflex AVS class 3 driver does not require to use interrupts
and is not impacted by this change.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>