of/platform: Disable generic device linking code for PowerPC

PowerPC platforms don't use the generic of/platform code to populate the
devices from DT.  Therefore the generic device linking code is never used
in PowerPC.  Compile it out to avoid warning about unused functions.

If a specific PowerPC platform wants to use this code in the future,
bringing this back for PowerPC would be trivial. We'll just need to export
of_link_to_suppliers() and then let the machine specific files do the
linking as they populate the devices from DT.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20190806192654.138605-2-saravanak@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>