clk: implement clk_set_defaults()

Linux uses the properties 'assigned-clocks', 'assigned-clock-parents'
and 'assigned-clock-rates' to configure the clock subsystem for use
with various peripheral nodes.

This implements clk_set_defaults() and hooks it up with the general
device probibin in drivers/core/device.c: when a new device is probed,
clk_set_defaults() will be called for it and will process the
properties mentioned above.

Note that this functionality is designed to fail gracefully (i.e. if a
clock-driver does not implement set_parent(), we simply accept this
and ignore the error) as not to break existing board-support.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: David Wu <david.wu@rock-chips.com>

Series-changes: 2
- Fixed David's email address.

Series-version: 2

Cover-letter:
clk: support assigned-clock, assigned-clock-parents, assigned-clock-rates

For various peripherals on Rockchip SoCs (e.g. for the Ethernet GMAC),
the parent-clock needs to be set via the DTS.  This adds the required
plumbing and implements the GMAC case for the RK3399.
END

drivers/core/device.c

@@ -11,6 +11,7 @@
 
 #include <common.h>
 #include <asm/io.h>
+#include <clk.h>
 #include <fdtdec.h>
 #include <fdt_support.h>
 #include <malloc.h>
@@ -391,6 +392,11 @@ int device_probe(struct udevice *dev)
 			goto fail;
 	}
 
+	/* Process 'assigned-{clocks/clock-parents/clock-rates}' properties */
+	ret = clk_set_defaults(dev);
+	if (ret)
+		goto fail;
+
 	if (drv->probe) {
 		ret = drv->probe(dev);
 		if (ret) {