soc/intel/fsp-car: Use the coreboot defined stack

The stack needs to be in the coreboot defined region to not collide
with other symbols.

Change-Id: I02a379d2ac73ae30239bd45859c3f09de1a9d0e0
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37278
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>

src/soc/intel/common/block/cpu/car/cache_as_ram_fsp.S

@@ -71,7 +71,7 @@ CAR_init_done:
 	jnz	.halt_forever
 
 	/* Setup bootblock stack */
-	mov	%edx, %esp
+	movl	$_ecar_stack, %esp
 	/*
 	 * temp_memory_start/end reside in the .bss section, which gets cleared
 	 * below. Save the FSP return value to the stack before writing those