cmd: add a panic command

Even in boot scripts it may be needed to "panic" when all options
are exhausted and the device specification specifies hanging
instead of resetting the board.

So add a new panic command that just wraps around the core panic
call in U-Boot and can take an optional message.
Signed-off-by: NHeiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NTom Rini <trini@konsulko.com>

cmd/Makefile

@@ -8,6 +8,7 @@ ifndef CONFIG_SPL_BUILD
 obj-y += boot.o
 obj-$(CONFIG_CMD_BOOTM) += bootm.o
 obj-y += help.o
+obj-y += panic.o
 obj-y += version.o
 
 # command

cmd/panic.c

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2020 Theobroma Systems Design und Consulting GmbH
+ */
+
+#include <common.h>
+#include <command.h>
+
+static int do_panic(struct cmd_tbl *cmdtp, int flag, int argc,
+		    char * const argv[])
+{
+	char *text = (argc < 2) ? "" : argv[1];
+
+	panic(text);
+
+	return CMD_RET_SUCCESS;
+}
+
+U_BOOT_CMD(
+	panic,	2,	1,	do_panic,
+	"Panic with optional message",
+	"[message]"
+);