firmware: arm_scmi: Add SMCCC discovery dependency in Kconfig

ARM_SCMI_PROTOCOL depends on either MAILBOX or HAVE_ARM_SMCCC_DISCOVERY,
not MAILBOX alone. Fix the depedency in Kconfig file and driver to
reflect the same.

Link: https://lore.kernel.org/r/20210521134055.24271-1-etienne.carriere@linaro.org
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
[sudeep.holla: Minor tweaks to subject and change log]
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/Kconfig

@@ -9,7 +9,7 @@ menu "Firmware Drivers"
 config ARM_SCMI_PROTOCOL
 	tristate "ARM System Control and Management Interface (SCMI) Message Protocol"
 	depends on ARM || ARM64 || COMPILE_TEST
-	depends on MAILBOX
+	depends on MAILBOX || HAVE_ARM_SMCCC_DISCOVERY
 	help
 	  ARM System Control and Management Interface (SCMI) protocol is a
 	  set of operating system-independent software interfaces that are

drivers/firmware/arm_scmi/common.h

@@ -331,7 +331,7 @@ struct scmi_desc {
 };
 
 extern const struct scmi_desc scmi_mailbox_desc;
-#ifdef CONFIG_HAVE_ARM_SMCCC
+#ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
 extern const struct scmi_desc scmi_smc_desc;
 #endif