pwm: atmel: Remove platform_device_id and use only dt bindings

Since commit 26202873 ("avr32: remove support for AVR32
architecture") there is no more user of platform_device_id and we
should only use dt bindings

Signed-off-by: Kamel Bouhara <kamel.bouhara@bootlin.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>