firmware: smccc: Fix missing prototype warning for arm_smccc_version_init

Commit f2ae9706 ("firmware: smccc: Refactor SMCCC specific bits into
separate file") introduced the following build warning:

drivers/firmware/smccc/smccc.c:14:13: warning: no previous prototype for
	function 'arm_smccc_version_init' [-Wmissing-prototypes]
 void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit)
             ^~~~~~~~~~~~~~~~~~~~~~

Fix the same by adding the missing prototype in arm-smccc.h
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20200521110836.57252-1-sudeep.holla@arm.comSigned-off-by: Will Deacon <will@kernel.org>

drivers/firmware/psci/psci.c

@@ -79,7 +79,6 @@ static u32 psci_function_id[PSCI_FN_MAX];
 
 static u32 psci_cpu_suspend_feature;
 static bool psci_system_reset2_supported;
-void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit);
 
 static inline bool psci_has_ext_power_state(void)
 {

include/linux/arm-smccc.h

@@ -5,6 +5,7 @@
 #ifndef __LINUX_ARM_SMCCC_H
 #define __LINUX_ARM_SMCCC_H
 
+#include <linux/init.h>
 #include <uapi/linux/const.h>
 
 /*
@@ -111,6 +112,8 @@ enum arm_smccc_conduit arm_smccc_1_1_get_conduit(void);
  */
 u32 arm_smccc_get_version(void);
 
+void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit);
+
 /**
  * struct arm_smccc_res - Result from SMC/HVC call
  * @a0-a3 result values from registers 0 to 3