watchdog: at91rm9200: use the system timer syscon

Use a syscon regmap to access the system timer registers.

Also, rename the driver atmel_st_watchdog to stop conflicting with
at91sam9_wdt.c

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 16f2023..ce4f3a7 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -154,7 +154,7 @@
 
 config AT91RM9200_WATCHDOG
 	tristate "AT91RM9200 watchdog"
-	depends on SOC_AT91RM9200
+	depends on SOC_AT91RM9200 && MFD_SYSCON
 	help
 	  Watchdog timer embedded into AT91RM9200 chips. This will reboot your
 	  system when the timeout is reached.