Blackfin: add an early shadow console

Add a memory based shadow console to keep a copy of the printk buffer in a
location which can be found externally.  This allows bootloaders to locate
and utilize the log buffer in case of silent (early/resume/etc...) crashes.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/include/asm/early_printk.h

@@ -23,6 +23,8 @@
 
 #ifdef CONFIG_EARLY_PRINTK
 extern int setup_early_printk(char *);
+extern void enable_shadow_console(void);
 #else
 #define setup_early_printk(fmt) do { } while (0)
+#define enable_shadow_console(fmt)  do { } while (0)
 #endif /* CONFIG_EARLY_PRINTK */