reset: Add driver for gpio-controlled reset pins

reset: Add driver for gpio-controlled reset pins

This driver implements a reset controller device that toggles gpios
connected to reset pins of peripheral ICs. The delay between assertion
and de-assertion of the reset signal can be configured.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Pavel Machek <pavel@ucw.cz>