PM / OPP: Hide OPP configuration when SoCs do not provide an implementation

Since the OPP API is only useful with an appropraite SoC-specific
implementation there is no point in offering the ability to enable
the API on general systems. Provide an ARCH_HAS OPP Kconfig symbol
which masks out the option unless selected by an implementation.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/Documentation/power/opp.txt b/Documentation/power/opp.txt
index 44d87ad..cd44558 100644
--- a/Documentation/power/opp.txt
+++ b/Documentation/power/opp.txt
@@ -37,6 +37,9 @@
 SoC framework	-> modifies on required cases certain OPPs	-> OPP layer
 		-> queries to search/retrieve information	->
 
+Architectures that provide a SoC framework for OPP should select ARCH_HAS_OPP
+to make the OPP layer available.
+
 OPP layer expects each domain to be represented by a unique device pointer. SoC
 framework registers a set of initial OPPs per device with the OPP layer. This
 list is expected to be an optimally small number typically around 5 per device.