Added use of runtime PM autosuspend feature, with a fixed
timeout of 50 ms. This will prevent adding a latency,
although very minor, for _every_ request.

Moreover the runtime_get_sync is now also used in set_ios and
suspend since the runtime resourses are needed here as well.
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>