power/reset: at91-poweroff: allow compiling as a module

It was not possible to compile at91-poweroff as a module. Implement
.remove() to allow it. Also switch to module_platform_driver_probe() as it
is not hotpluggable.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

drivers/power/reset/Kconfig

@@ -15,7 +15,7 @@ config POWER_RESET_AS3722
 	  This driver supports turning off board via a ams AS3722 power-off.
 
 config POWER_RESET_AT91_POWEROFF
-	bool "Atmel AT91 poweroff driver"
+	tristate "Atmel AT91 poweroff driver"
 	depends on ARCH_AT91
 	default SOC_AT91SAM9 || SOC_SAMA5
 	help

drivers/power/reset/at91-poweroff.c

@@ -119,7 +119,7 @@ static void at91_poweroff_dt_set_wakeup_mode(struct platform_device *pdev)
 	writel(wakeup_mode | mode, at91_shdwc_base + AT91_SHDW_MR);
 }
 
-static int at91_poweroff_probe(struct platform_device *pdev)
+static int __init at91_poweroff_probe(struct platform_device *pdev)
 {
 	struct resource *res;
 
@@ -140,6 +140,14 @@ static int at91_poweroff_probe(struct platform_device *pdev)
 	return 0;
 }
 
+static int __exit at91_poweroff_remove(struct platform_device *pdev)
+{
+	if (pm_power_off == at91_poweroff)
+		pm_power_off = NULL;
+
+	return 0;
+}
+
 static const struct of_device_id at91_poweroff_of_match[] = {
 	{ .compatible = "atmel,at91sam9260-shdwc", },
 	{ .compatible = "atmel,at91sam9rl-shdwc", },
@@ -148,10 +156,14 @@ static const struct of_device_id at91_poweroff_of_match[] = {
 };
 
 static struct platform_driver at91_poweroff_driver = {
-	.probe = at91_poweroff_probe,
+	.remove = __exit_p(at91_poweroff_remove),
 	.driver = {
 		.name = "at91-poweroff",
 		.of_match_table = at91_poweroff_of_match,
 	},
 };
-module_platform_driver(at91_poweroff_driver);
+module_platform_driver_probe(at91_poweroff_driver, at91_poweroff_probe);
+
+MODULE_AUTHOR("Atmel Corporation");
+MODULE_DESCRIPTION("Shutdown driver for Atmel SoCs");
+MODULE_LICENSE("GPL v2");