reset: imx7: Support module build

Use module_platform_driver(), add module device table, author,
description and license to support module build, and
CONFIG_RESET_IMX7 is changed to default 'y' ONLY for i.MX7D,
other platforms need to select it in defconfig.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>