PWM on D13 does not work with arduino_mzero variant

[tbowmo]

Pin configuration is missing PIN_ATTR_TIMER, in order to get PWM working on the channel

{ PORTA, 17, PIO_PWM, (PIN_ATTR_DIGITAL|PIN_ATTR_PWM|PIN_ATTR_TIMER), No_ADC_Channel, PWM2_CH1, TCC2_CH1, EXTERNAL_INT_1 }, // TCC2/WO[1]

Above is copied from arduino_zero variant.

[tbowmo]

Probably issues with D6/D7 as well, as they are configured to use PIN_ATTR_TIMER, and not PIN_ATTR_TIMER_ALT (like arduino_zero variant)