ARM: dts: lpc32xx: Set motor PWM #pwm-cells property value to 3 cells

ARM: dts: lpc32xx: Set motor PWM #pwm-cells property value to 3 cells

Since commit 4cd2f417a0ac ("dt-bindings: pwm: Convert lpc32xx-pwm.txt
to yaml format") both types of PWM controlles on NXP LPC32xx SoC
fairly gained 3 cells, reflect it in the platform dtsi file.

The change removes a dt binding checker warning:

    mpwm@400e8000: #pwm-cells:0:0: 3 was expected

Cc: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>