AMD boards: Fix romstage main() declaration

Boards incorrectly used intel include file for AMD board.

Change-Id: I6d3172d1aa5c91c989a6ef63066a7cd6f70013f5
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15232
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/cpu/amd/car.h

@@ -1,6 +1,8 @@
 #ifndef _CPU_AMD_CAR_H
 #define _CPU_AMD_CAR_H
 
+void main(unsigned long bist);
+
 void cache_as_ram_main(unsigned long bist, unsigned long cpu_init_detectedx);
 void done_cache_as_ram_main(void);
 void post_cache_as_ram(void);