firmware: scmi: add configs to select the supported agents

Add two configs CONFIG_SCMI_AGENT_MAILBOX and CONFIG_SCMI_AGENT_SMCCC
to select the supported agents as all the agents are not supported.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Acked-by: Etienne Carriere <etienne.carriere@linaro.org>
diff --git a/drivers/firmware/scmi/Kconfig b/drivers/firmware/scmi/Kconfig
index c3a109b..c33de87 100644
--- a/drivers/firmware/scmi/Kconfig
+++ b/drivers/firmware/scmi/Kconfig
@@ -17,3 +17,19 @@
 	  based on message exchange. Messages can be exchange over tranport
 	  channels as a mailbox device or an Arm SMCCC service with some
 	  piece of identified shared memory.
+
+config SCMI_AGENT_MAILBOX
+	bool "Enable SCMI agent mailbox"
+	depends on SCMI_FIRMWARE && DM_MAILBOX
+	default y
+	help
+	  Enable the SCMI communication channel based on mailbox
+	  for compatible "arm,scmi".
+
+config SCMI_AGENT_SMCCC
+	bool "Enable SCMI agent SMCCC"
+	depends on SCMI_FIRMWARE && ARM_SMCCC
+	default y
+	help
+	  Enable the SCMI communication channel based on Arm SMCCC service for
+	  compatible "arm,scmi-smc".