AGESA,binaryPI: Fix stack location on entry to romstage

For BSP CPU, set up stack location to match the symbol from car.ld.
For AP CPUs the stack is located outside _car_region and is currently
not accounted for in the linker scripts.

Change-Id: I0ec84ae4e73ecca5034f799cdc2a5c1056ad8b74
Signed-off-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37351
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/include/cpu/amd/car.h

@@ -4,5 +4,6 @@
 #include <arch/cpu.h>
 
 asmlinkage void romstage_main(unsigned long bist);
+asmlinkage void ap_romstage_main(void);
 
 #endif