cmd: xxd: add new command

Add xxd command to print file content as hexdump to standard out

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Roger Knecht <rknecht@pm.me>
diff --git a/cmd/Makefile b/cmd/Makefile
index 4bd52bb..d9bbd0b 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -185,6 +185,7 @@
 obj-$(CONFIG_CMD_THOR_DOWNLOAD) += thordown.o
 obj-$(CONFIG_CMD_VBE) += vbe.o
 obj-$(CONFIG_CMD_XIMG) += ximg.o
+obj-$(CONFIG_CMD_XXD) += xxd.o
 obj-$(CONFIG_CMD_YAFFS2) += yaffs2.o
 obj-$(CONFIG_CMD_SPL) += spl.o
 obj-$(CONFIG_CMD_W1) += w1.o