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/Makefile b/drivers/Makefile
index d532085..d296354 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -103,6 +103,7 @@
 obj-y += soc/
 obj-$(CONFIG_REMOTEPROC) += remoteproc/
 obj-y += thermal/
+obj-y += axi/
 
 obj-$(CONFIG_MACH_PIC32) += ddr/microchip/
 endif