interrupts is listed as an optional property in the DT
binding, but in reality the driver didn't work without it.
The existing driver relied on having the interrupt line
connected to the SoC to trigger handling various events.

Add the option to poll the interrupt status register via
a timer if no interrupt source is defined.
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>