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/MAINTAINERS b/MAINTAINERS
index 1c9939e..cb4d445 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1519,6 +1519,13 @@
 S:	Maintained
 F:	arch/xtensa/
 
+XXD
+M:	Roger Knecht <rknecht@pm.me>
+S:	Maintained
+F:	cmd/xxd.c
+F:	doc/usage/cmd/xxd.rst
+F:	test/py/tests/test_xxd/
+
 THE REST
 M:	Tom Rini <trini@konsulko.com>
 L:	u-boot@lists.denx.de