cmd: xxd: move xxd into shell commands

Move xxd into shell command section.

Signed-off-by: Roger Knecht <rknecht@pm.me>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/Kconfig

@@ -500,11 +500,6 @@ config CMD_XIMG
 	help
 	  Extract a part of a multi-image.
 
-config CMD_XXD
-	bool "xxd"
-	help
-	  Print file as hexdump to standard output
-
 config CMD_SPL
 	bool "spl export - Export boot information for Falcon boot"
 	depends on SPL
@@ -1668,6 +1663,11 @@ config CMD_SETEXPR_FMT
 	  Evaluate format string expression and store result in an environment
 	    variable.
 
+config CMD_XXD
+	bool "xxd"
+	help
+	  Print file as hexdump to standard output
+
 endmenu
 
 menu "Android support commands"