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/kernel/setup.c

@@ -810,6 +810,8 @@ void __init setup_arch(char **cmdline_p)
 {
 	unsigned long sclk, cclk;
 
+	enable_shadow_console();
+
 	/* Check to make sure we are running on the right processor */
 	if (unlikely(CPUID != bfin_cpuid()))
 		printk(KERN_ERR "ERROR: Not running on ADSP-%s: unknown CPUID 0x%04x Rev 0.%d\n",