cmd: Add axi command

Add a command to debug the AXI bus.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index ef43ed8..bd90946 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1027,6 +1027,14 @@
 	help
 	  USB mass storage support
 
+config CMD_AXI
+	bool "axi"
+	depends on AXI
+	help
+	  Enable the command "axi" for accessing AXI (Advanced eXtensible
+	  Interface) busses, a on-chip interconnect specification for managing
+	  functional blocks in SoC designs, which is also often used in designs
+	  involving FPGAs (e.g.  communication with IP cores in Xilinx FPGAs).
 endmenu