greybus: kernel_ver: add handle for lights in 4.5

In v4.5 the LED API is changed related to the set brightness
operations, set_sync is removed and the workqueue handling is now done
by leds core, so no need for individual drivers to have one.
This will be done by removing the SET_SYNC macro and add a new
SET_BLOCKING.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>