ARM: at91: at91sam9m10g45ek: switch to PWM leds

The d6 and d7 is connected to PWM, we can use PWM to control it,
so switch to PWM leds.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>