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

include/clk.h

@@ -133,6 +133,23 @@ static inline int clk_release_all(struct clk *clk, int count)
 
 #endif
 
+#if (CONFIG_IS_ENABLED(OF_CONTROL) && !CONFIG_IS_ENABLED(OF_PLATDATA)) && \
+	CONFIG_IS_ENABLED(CLK)
+/**
+ * clk_set_defaults - Process 'assigned-{clocks/clock-parents/clock-rates}'
+ *                    properties to configure clocks
+ *
+ * @dev:        A device to process (the ofnode associated with this device
+ *              will be processed).
+ */
+int clk_set_defaults(struct udevice *dev);
+#else
+static inline int clk_set_defaults(struct udevice *dev)
+{
+	return 0;
+}
+#endif
+
 /**
  * clk_request - Request a clock by provider-specific ID.
  *