Add support for the tracing infastructure in coreboot.

The compiler is forced to emmit special functions on every
entry/exit of the function. Add a compile time option
to support it. Function entries will be printed in
the console. The CONFIG_TRACE has more documentation.

Patch for userspace tools will follow.

Change-Id: I2cbeb3f104892b034c8756f86ed05bf71187c3f3
Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Reviewed-on: http://review.coreboot.org/178
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/console/printk.c

@@ -8,6 +8,7 @@
 #include <smp/spinlock.h>
 #include <console/vtxprintf.h>
 #include <console/console.h>
+#include <trace.h>
 
 int console_loglevel = CONFIG_DEFAULT_CONSOLE_LOGLEVEL;
 int default_console_loglevel = CONFIG_DEFAULT_CONSOLE_LOGLEVEL;
@@ -23,6 +24,7 @@ int do_printk(int msg_level, const char *fmt, ...)
 		return 0;
 	}
 
+	DISABLE_TRACE;
 	spin_lock(&console_lock);
 
 	va_start(args, fmt);
@@ -32,6 +34,7 @@ int do_printk(int msg_level, const char *fmt, ...)
 	console_tx_flush();
 
 	spin_unlock(&console_lock);
+	ENABLE_TRACE;
 
 	return i;
 }