Before things go out of hand, make it possible to pass
flags when requesting "own" descriptors from a gpio_chip.
This is necessary if the chip wants to request a GPIO with
active low semantics, for example.

Cc: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Roger Quadros <rogerq@ti.com>
Reviewed-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>