arm64: dts: imx8mq: Add pwm device nodes

We can reuse the pwm from fsl,imx27-pwm as with other imx SOCs.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>