xtensa: add support for the 'xtfpga' evaluation board

The 'xtfpga' board is actually a set of FPGA evaluation boards that
can be configured to run an Xtensa processor.

 - Avnet Xilinx LX60
 - Avnet Xilinx LX110
 - Avnet Xilinx LX200
 - Xilinx ML605
 - Xilinx KC705

These boards share the same components (open-ethernet, ns16550 serial,
lcd display, flash, etc.).

Signed-off-by: Chris Zankel <chris@zankel.net>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/xtensa/dts/Makefile b/arch/xtensa/dts/Makefile
index eacf6f3..e14cdac 100644
--- a/arch/xtensa/dts/Makefile
+++ b/arch/xtensa/dts/Makefile
@@ -2,6 +2,8 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+dtb-$(CONFIG_XTFPGA) += ml605.dtb ml605_nommu.dtb kc705.dtb kc705_nommu.dtb
+
 targets += $(dtb-y)
 
 DTC_FLAGS +=