avr32/at32ap: switch to the generic PWM framework

Switch to the pwm/pwm-atmel driver instead of misc/atmel_pwm

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>