rtc-at91rm9200: use shadow IMR on at91sam9x5

Add support for the at91sam9x5-family which must use the shadow
interrupt mask due to a hardware issue (causing RTC_IMR to always be
zero).
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: Robert Nelson <Robert.Nelson@digikey.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/devicetree/bindings/rtc/atmel,at91rm9200-rtc.txt

 Atmel AT91RM9200 Real Time Clock
 
 Required properties:
-- compatible: should be: "atmel,at91rm9200-rtc"
+- compatible: should be: "atmel,at91rm9200-rtc" or "atmel,at91sam9x5-rtc"
 - reg: physical base address of the controller and length of memory mapped
   region.
 - interrupts: rtc alarm/event interrupt

drivers/rtc/rtc-at91rm9200.c

@@ -309,11 +309,18 @@ static irqreturn_t at91_rtc_interrupt(int irq, void *dev_id)
 static const struct at91_rtc_config at91rm9200_config = {
 };
 
+static const struct at91_rtc_config at91sam9x5_config = {
+	.use_shadow_imr	= true,
+};
+
 #ifdef CONFIG_OF
 static const struct of_device_id at91_rtc_dt_ids[] = {
 	{
 		.compatible = "atmel,at91rm9200-rtc",
 		.data = &at91rm9200_config,
+	}, {
+		.compatible = "atmel,at91sam9x5-rtc",
+		.data = &at91sam9x5_config,
 	}, {
 		/* sentinel */
 	}