AGESA: Disable CAR with empty stack

Calling disable_cache_as_ram() with valuables in stack is not
a stable solution, as per documentation AMD_DISABLE_STACK
should destroy stack in cache.

Change-Id: I986bb7a88f53f7f7a0b05d4edcd5020f5dbeb4b7
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/18626
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/cpu/amd/car.h

@@ -19,5 +19,6 @@ void disable_cache_as_ram(void);
 void asmlinkage early_all_cores(void);
 
 void * asmlinkage romstage_main(unsigned long bist);
+void asmlinkage romstage_after_car(void);
 
 #endif