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>

cmd/Kconfig

@@ -952,6 +952,16 @@ endmenu
 
 menu "Device access commands"
 
+config CMD_ARMFFA
+	bool "Arm FF-A test command"
+	depends on ARM_FFA_TRANSPORT
+	help
+	  Provides a test command for the FF-A support
+	  supported options:
+		- Listing the partition(s) info
+		- Sending a data pattern to the specified partition
+		- Displaying the arm_ffa device info
+
 config CMD_ARMFLASH
 	#depends on FLASH_CFI_DRIVER
 	bool "armflash"