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/kernel/power/Kconfig b/kernel/power/Kconfig
index 29bff61..a5aff3e 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -246,9 +246,13 @@
 	depends on PM_SLEEP || PM_RUNTIME
 	default y
 
+config ARCH_HAS_OPP
+	bool
+
 config PM_OPP
 	bool "Operating Performance Point (OPP) Layer library"
 	depends on PM
+	depends on ARCH_HAS_OPP
 	---help---
 	  SOCs have a standard set of tuples consisting of frequency and
 	  voltage pairs that the device will support per voltage domain. This