mkimage: Report information about fpga

Add FIT_FPGA_PROP that user can identify an optional
entry for fpga.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/image.c b/common/image.c
index 9824685..ec78b7e 100644
--- a/common/image.c
+++ b/common/image.c
@@ -160,6 +160,7 @@
 	{	IH_TYPE_RKSPI,      "rkspi",      "Rockchip SPI Boot Image" },
 	{	IH_TYPE_ZYNQIMAGE,  "zynqimage",  "Xilinx Zynq Boot Image" },
 	{	IH_TYPE_ZYNQMPIMAGE, "zynqmpimage", "Xilinx ZynqMP Boot Image" },
+	{	IH_TYPE_FPGA,       "fpga",       "FPGA Image" },
 	{	-1,		    "",		  "",			},
 };