ARM: dts: at91: sama5d2_xplained: add pinmuxing for pwm0

Add pin muxing for pwm0 and set it as disabled since it is in conflict
with pins for leds.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>