dt-bindings: reset: imx8mq: add m4 reset

Add the m4 reset used by the remoteproc driver

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>