arm_ffa: introduce armffa command

Provide armffa command showcasing the use of the U-Boot FF-A support

armffa is a command showcasing how to invoke FF-A operations.
This provides a guidance to the client developers on how to
call the FF-A bus interfaces. The command also allows to gather secure
partitions information and ping these  partitions. The command is also
helpful in testing the communication with secure partitions.

For more details please refer to the command documentation [1].

A Sandbox test is provided for the armffa command.

[1]: doc/usage/cmd/armffa.rst

Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jens Wiklander <jens.wiklander@linaro.org>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/drivers/firmware/arm-ffa/Kconfig b/drivers/firmware/arm-ffa/Kconfig
index fc668c1..d75f8b5 100644
--- a/drivers/firmware/arm-ffa/Kconfig
+++ b/drivers/firmware/arm-ffa/Kconfig
@@ -5,6 +5,7 @@
 	depends on DM && (ARM64 || SANDBOX)
 	select ARM_SMCCC if !SANDBOX
 	select ARM_SMCCC_FEATURES if !SANDBOX
+	imply CMD_ARMFFA
 	select LIB_UUID
 	select DEVRES
 	help