ARM: at91: cpuidle: Convert to platform driver

Using the platform driver model is a good way to separate the cpuidle specific
code from the low level pm code. It allows to remove the dependency between
these two components.

The platform_device is located in the pm code and a 'set' function has been
added to set the standby function from the AT91_SOC_START initialization
function. Each SoC with a cpuidle driver will set the standby function in the
platform_data field at init time. Then pm code will register the cpuidle
platform device.

The cpuidle driver will register the platform_driver and use the device's
platform_data as a standby callback in the idle path.

The at91_pm_enter function contains a { if then else } based on cpu_is_xx
similar to what was in cpuidle. This is considered dangerous when adding a new
SoC. Like the cpuidle driver, a standby ops is defined and assigned when the
SoC init function specifies what is its standby function and reused in the
at91_pm_enter's 'case' block.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/at91sam9rl.c

@@ -27,6 +27,7 @@
 #include "generic.h"
 #include "clock.h"
 #include "sam9_smc.h"
+#include "pm.h"
 
 /* --------------------------------------------------------------------
  *  Clocks
@@ -296,6 +297,8 @@ static void __init at91sam9rl_initialize(void)
 
 	/* Register GPIO subsystem */
 	at91_gpio_init(at91sam9rl_gpio, 4);
+
+	at91_pm_set_standby(at91sam9_standby);
 }
 
 /* --------------------------------------------------------------------