ARM: imx: register reset controller from a platform driver

Starting with commit 6b2117ad ("of: property: fw_devlink: Add
support for "resets" and "pwms""), the imx-drm driver fails to load
due to forever dormant devlinks to the reset-controller node. This
node was never associated with a struct device.

Add a platform device to allow fw_devnode to activate the devlinks.

Fixes: 6b2117ad

 ("of: property: fw_devlink: Add support for "resets" and "pwms"")
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>