bootblock: Provide some common prototypes

The split of bootblock initialisation to cpu, northbridge and
southbridge is not specific to intel at all, create new header
<arch/bootblock.h> as AMD will want some of these too.

Change-Id: I702cc6bad4afee4f61acf58b9155608b28eb417e
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37429
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/cpu/intel/model_206ax/bootblock.c

@@ -12,11 +12,11 @@
  */
 
 #include <stdint.h>
+#include <arch/bootblock.h>
 #include <arch/cpu.h>
 #include <cpu/x86/msr.h>
 #include <arch/io.h>
 #include <halt.h>
-#include <cpu/intel/car/bootblock.h>
 
 #include "model_206ax.h"