smccc: define generic IDs for feature discovery

Defines function IDs ARM_SMCCC_ARCH_FEATURES used to query SMCCC feature
support, applicable from Arm SMCCC v1.1 specification.

Defines macro ARM_SMCCC_RET_NOT_SUPPORTED as generic return identifier
for when a SMCCC feature is not supported.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index 7f2be23..94a20c9 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -51,6 +51,10 @@
 #define ARM_SMCCC_QUIRK_NONE		0
 #define ARM_SMCCC_QUIRK_QCOM_A6		1 /* Save/restore register a6 */
 
+#define ARM_SMCCC_ARCH_FEATURES		0x80000001
+
+#define ARM_SMCCC_RET_NOT_SUPPORTED	((unsigned long)-1)
+
 #ifndef __ASSEMBLY__
 
 #include <linux/linkage.h>