regulator: core: Add new notification for enabling of regulator

This is useful for devices, which need some time to start up, to help
the drivers track how long the supply has been up already. Ie whether
it can safely talk to the HW or needs to wait.

Signed-off-by: Harald Geyer <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/core.c

···
 			if (ret < 0)
 				return ret;
 
+			_notifier_call_chain(rdev, REGULATOR_EVENT_ENABLE,
+					     NULL);
 		} else if (ret < 0) {
 			rdev_err(rdev, "is_enabled() failed: %d\n", ret);
 			return ret;

include/linux/regulator/consumer.h

···
 #define REGULATOR_EVENT_ABORT_VOLTAGE_CHANGE	0x200
 #define REGULATOR_EVENT_PRE_DISABLE		0x400
 #define REGULATOR_EVENT_ABORT_DISABLE		0x800
+#define REGULATOR_EVENT_ENABLE			0x1000
 
 /*
  * Regulator errors that can be queried using regulator_get_error_flags