regulator: act8945a-regulator: add shutdown function

Implement shutdown method to make sure the PMIC will not enter the suspend
state when the system is shutdown.

This work is based on work done by Borris Brezillon on [1].

[1] https://www.spinics.net/lists/kernel/msg2942960.html

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/act8945a-regulator.c

@@ -339,12 +339,23 @@ static int act8945a_suspend(struct device *pdev)
 
 SIMPLE_DEV_PM_OPS(act8945a_pm, act8945a_suspend, NULL);
 
+static void act8945a_pmic_shutdown(struct platform_device *pdev)
+{
+	struct act8945a_pmic *act8945a = platform_get_drvdata(pdev);
+
+	/*
+	 * Ask the PMIC to shutdown everything on the next PWRHLD transition.
+	 */
+	regmap_write(act8945a->regmap, ACT8945A_SYS_CTRL, 0x0);
+}
+
 static struct platform_driver act8945a_pmic_driver = {
 	.driver = {
 		.name = "act8945a-regulator",
 		.pm = &act8945a_pm,
 	},
 	.probe = act8945a_pmic_probe,
+	.shutdown = act8945a_pmic_shutdown,
 };
 module_platform_driver(act8945a_pmic_driver);