drivers: Add AXI uclass

Add a uclass for AXI (Advanced eXtensible Interface) busses, and a
driver for the gdsys IHS AXI bus on IHS FPGAs.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/axi/Makefile b/drivers/axi/Makefile
new file mode 100644
index 0000000..100a777
--- /dev/null
+++ b/drivers/axi/Makefile
@@ -0,0 +1,8 @@
+#
+# (C) Copyright 2017
+# Mario Six,  Guntermann & Drunck GmbH, mario.six@gdsys.cc
+#
+# SPDX-License-Identifier:	GPL-2.0+
+#
+
+obj-$(CONFIG_AXI) += axi-uclass.o