Create an interface for drivers to enable or disable their clocks as listed
in the clocks=<...> properties of their FDT data.  The clock properties
consist of 2-cell tuples, each containing a clock device node reference and
a clock number.  A clock device driver can register itself as providing
this interface, then other drivers can turn the FDT clock node reference
into the corresponding device_t so that they can use the interface to query
and manipulate their clocks.

This provides convenience functions to enable or disable all the clocks
listed in the properties for a device, so most drivers will be able to
manage their clocks with a single call to fdt_clock_enable_all(dev).