Remove the cmd_ prefix from command files

Now that they are in their own directory, we can remove this prefix.
This makes it easier to find a file since the prefix does not get in the
way.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Acked-by: Stefan Roese <sr@denx.de>
Acked-by: Przemyslaw Marczak <p.marczak@samsung.com>

cmd/exit.c

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2000-2009
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <command.h>
+
+static int do_exit(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	int r;
+
+	r = 0;
+	if (argc > 1)
+		r = simple_strtoul(argv[1], NULL, 10);
+
+	return -r - 2;
+}
+
+U_BOOT_CMD(
+	exit,	2,	1,	do_exit,
+	"exit script",
+	""
+);