ARM64: dts: imx8mp-evk: add pwm support

Enable pwm1/2/4 support.
Enable pwm1 on pin GPIO1_IO01 for DSI_BL_PWM
       pwm2 on pin GPIO1_IO11 for LVDS_BL_PWM
       pwm4 on pin SAI5_RXFS for J21-32

Acked-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>