dm: Add a power sequencing uclass

Some devices need special sequences to be used when starting up. Add a
uclass for this. Drivers can be added to provide specific features as
needed.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/pwrseq.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __pwrseq_h
+#define __pwrseq_h
+
+struct pwrseq_ops {
+	int (*set_power)(struct udevice *dev, bool enable);
+};
+
+#define pwrseq_get_ops(dev)	((struct pwrseq_ops *)(dev)->driver->ops)
+
+int pwrseq_set_power(struct udevice *dev, bool enable);
+
+#endif