Add a dedicated panic() function

In addition to ASSERT(), it might be useful to panic() sometimes, so add
a tidy way of doing it which will print a message and reset.

BUG=chrome-os-partner:10149
TEST=manual
Build a special version for snow where the 'rw' command calls panic()
See that a message is produced:
> rw 0
read 0x0 = 0x20001048

** PANIC: Address is 0

Change-Id: I4512c0193f4c1d52d0c256b2deefacf551056fd9
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/25413

core/cortex-m/panic.c

@@ -372,3 +372,9 @@ void panic_assert_fail(const char *msg, const char *func, const char *fname,
 	panic_reboot();
 }
 #endif
+
+
+void panic(const char *msg)
+{
+	report_panic(msg, NULL);
+}

include/panic.h

@@ -68,6 +68,13 @@ void panic_printf(const char *format, ...);
 void panic_assert_fail(const char *msg, const char *func, const char *fname,
 		       int linenum);
 
+/**
+ * Display a panic message and reset
+ *
+ * @param msg	Panic message
+ */
+void panic(const char *msg);
+
 /**
  * Report a panic to the panic reporting device
  *