powerpc: Add SCOM infrastructure

SCOM is a side-band configuration bus implemented on some processors.
This code provides a way for code to map and operate on devices via
SCOM, while the details of how that is implemented is left up to a
SCOM "controller" in the platform code.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/sysdev/Kconfig b/arch/powerpc/sysdev/Kconfig
index cfc1877..d775fd1 100644
--- a/arch/powerpc/sysdev/Kconfig
+++ b/arch/powerpc/sysdev/Kconfig
@@ -15,3 +15,10 @@
 
 source "arch/powerpc/sysdev/xics/Kconfig"
 
+config PPC_SCOM
+	bool
+
+config SCOM_DEBUGFS
+	bool "Expose SCOM controllers via debugfs"
+	depends on PPC_SCOM
+	default n