[media] omap4iss: Use a common macro for all sleep-based poll loops

Instead of implementing usleep_range-based poll loops manually (and
slightly differently), create a generic iss_poll_wait_timeout() macro
and use it through the driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>